Recent concepts in patellofemoral instability Nishant D. Merchanta and Craig H. Bennettb
Purpose of review Recent patellofemoral literature on biomechanical and anatomical analyses, imaging studies, acute and chronic instability treatment, and patellar realignment procedures will be reviewed. Recent findings A recent epidemiological study found women aged 10–17 years to be most predisposed to acute and recurrent patellar instability. Instability is experienced most readily at 208 of flexion where vastus medialis obliquus tension is also the least. A decreased Q-angle, however, improved resistance to lateral patellar tracking more than strengthening of the vastus medialis obliquus. Although conservative is still recommended for treatment primary dislocations, chronic instability is better treated with surgery. Mini-open medial reefing with lateral release, vastus lateralis tendon release, and medial patellofemoral ligament reconstruction have all showed promising results. Cadaveric studies facilitated the improved outcomes by helping us determine the isometric point of the medial patellofemoral ligament. Distal realignment procedures such as the Elmslie–Trillat and modified Roux–Goldthwait procedure have also improved outcomes in the proper population. Interestingly, patients with trochlear dysplasia benefited from proximal and distal realignment procedures more conclusively than by undergoing trochleoplasty. Summary Understanding the anatomy and biomechanics of the patellofemoral joint will guide future testing and treatment methods. Patellar realignment procedures are successful in managing recurrent instability; arthrosis and pain, however, are less controlled. Keywords lateral release, medial patellofemoral ligament, patella alta, patellofemoral instability, proximal and distal realignment, tibial tubercle osteotomy, vastus medialis obliquus Curr Opin Orthop 18:153–160. ß 2007 Lippincott Williams & Wilkins. a University of Maryland School of Medicine and bUniversity of Maryland Orthopaedics, Baltimore, Maryland, USA
Correspondence to Craig H. Bennett, 22 S. Greene Street, S11B, Baltimore, MD 21201, USA Tel: +1 410 328 6040; fax: +1 410 328 0534; e-mail:
[email protected]
Abbreviations MPFL VMO
medial patellofemoral ligament vastus medialis obliquus
ß 2007 Lippincott Williams & Wilkins 1041-9918
Introduction Patellofemoral instability generally occurs in individuals with altered anatomy, abnormal joint morphology, or increased generalized ligamentous laxity. The action of simultaneous internal rotation of the femur, external rotation of the tibia, and initial knee flexion can produce lateral patellar subluxation or dislocation.
Patellofemoral anatomy and biomechanics It is at low degrees of flexion that the knee is least stable to lateral patellar movement [1]. Trochlear dysplasia and patella alta also predispose patients to dislocation. In addition to bony architecture, soft tissue balance around the knee is important. The medial patellofemoral ligament (MPFL) and vastus medialis obliquus (VMO) muscle provide static and dynamic resistance to lateral patellar movement, respectively. Sixty percent of the total force restraining lateral movement of the patella is provided by the MPFL. Meanwhile, the medial retinaculum itself provides very little stability [2,3]. Brunet et al. [4] evaluated elderly cadaver knees with normal patellofemoral anatomy to determine patellar tracking during quadriceps contraction. An equal number of male and female knees without patella alta or trochlear dysplasia were used. They measured patellar shift and tilt upon flexion. Their results showed that the patella shifted and tilted medially from 0 to 228 of flexion and then laterally until 908 of flexion. With concentric contraction they noticed that lateral patellar shift was greatest between 40 and 708 of flexion and lateral patellar tilt was greatest between 45 and 558 of flexion compared to eccentric contraction. Thus, for frank dislocation to occur, the patella must be displaced prior to entering the sulcus or at an angle below 228 by a forceful quadriceps contraction.
Current Opinion in Orthopaedics 2007, 18:153–160
Senavongse and Amis [1] mechanically studied elderly cadaver knees to determine the force needed to displace the patella with the quadriceps under tension. Four conditions were selected for the study: intact patellofemoral joint, VMO relaxed, flat lateral condyle (trochlear 153
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dysplasia), and ruptured medial retinaculum. Their results showed that the lowest restraining force, regardless of pathology, was at 208 of flexion. Relaxing the VMO, flattening the trochlea, and rupturing the medial retinaculum significantly reduced the lateral restraining force throughout flexion. The flattened trochlea produced the greatest decrease in restraining force throughout flexion. Meanwhile, rupturing the medial structures had the greatest decrease in resistance at extension. VMO contraction played a stronger role in patellar stability between 20 and 908 of flexion compared to 0–208 of flexion. Thus, the authors state that the VMO may have minimal impact in stabilizing the patella near extension. Limitations of this experiment include its performance in vitro, which does not present the knee joint as part of a larger system.
Acute versus recurrent patellar dislocations Factors that predispose individuals to acute dislocation are known and still being studied. There is less information regarding the risk factors that predisposes an individual to recurrent dislocation. Fithian et al. [5] enrolled patients in a single metropolitan area that either presented with an acute dislocation or a convincing history of an acute dislocation. Patients were separated into two groups: first-time dislocation and recurrent dislocations. This prospective cohort study followed patients for a period of 2–5 years. Their results showed that the 10–17-year-old female group was at highest risk for acute and recurrent patellar dislocation. Women presented with increased joint mobility and slightly higher femoral torsion. In the 18–29-year-old group, the risk of recurrent dislocation between men and women was the same. This age group was also more likely to present with recurrent dislocation than a firsttime dislocation. Overall, women and individuals in their 20s were more likely to present with recurrent patellar dislocation. The group that presented with recurrent patellar dislocation (79%) on initial visit was also more likely to present with a subsequent dislocation of either knee during the follow-up period than first-time patients (26%). The index knee during the first visit was more likely to re-dislocate than the nonindex knee. Indications for subsequent instability in the index knee were prior history of subluxation/dislocation and young age at time of first injury. On imaging studies, the authors noted that patients with a subsequent dislocation during follow-up showed less VMO and MPFL edema on initial MRI compared to nonrecurrent, first-time dislocations.
Operative versus nonoperative treatment In most acute, nontraumatic dislocations, nonoperative treatment is preferred. The initial management is physical therapy and monitored rehabilitation for quadriceps strengthening and medialization of forces of the
patella. Indications for surgery after acute dislocation are failure to improve with nonoperative care, osteochondral injury at time of dislocation, continued gross instability, injury to the MPFL–VMO mechanism, and high level athletes that suffered a nontraumatic dislocation [6]. Elias et al. [7] performed a computer simulation study to characterize the patellofemoral pressure distribution of weight-bearing movement. These values were used to simulate weight-bearing joint movement from 40–908 of flexion with an initial Q-angle of 258 (measured at extension) to simulate increased risk of pain and dislocation. Patellar tilt and shift were not manipulated by the operators. Operative treatment was modeled by medializing the tibial tuberosity to create a Q-angle of 158 and nonoperative treatment was demonstrated by increasing the force applied by the VMO. Through these actions they noticed that the decrease in Q-angle created a larger decrease in the lateral force exerted on the patella by the quadriceps than increasing VMO strength. They also noticed that both treatment methods decreased rotation and tilt of the patella laterally. The two methods, however, did not universally decrease patellofemoral pressure due to patellar anatomy. The limitation of this study is that the investigators only included healthy knee models (no patella alta or trochlear dysplasia) and that the testing range of 40–908 does not include the position of maximal patellar instability based on recent literature. The study by Nikku et al. [8] is a continuation of a study evaluating outcome differences in primary dislocators. The initial study showed no difference between open (proximal realignment) and closed (immobilization for 3 weeks) treatment methods. The present study is a follow-up at an average of 7 years. The inclusion criteria were primary dislocation less than 14 days old, no previous history of knee injury or surgery, and no osteochondral fractures needing repair. At an average of 7 years, 81% of patients treated conservatively had an opinion of excellent or good versus 67% of patients treated operatively. They used Kujala and Hughston visual analog scale VAS scores to compare the two groups. The outcomes were similar. They noted two risk factors for recurrent instability: initial contralateral instability and girls with an open tibial apophysis. Their recommendation is that proximal realignment surgery should not be performed on primary dislocations. Buchner et al. [9] retrospectively reviewed patients who sustained an acute primary traumatic patellar dislocation. The average age of the patients (56% men) at time of injury was 20.3 years and average follow-up was 8.1 years. All patients who were predisposed to recurrent patellar dislocation based on radiographic evidence, had previous knee surgery, or had dislocated the same or contralateral knee were excluded from the study. These individuals
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Patellofemoral instability Merchant and Bennett 155
were divided into groups based on their treatment plan: nonoperative treatment or simple arthroscopy to remove chondral or osteochondral fragments, immediate surgical reconstruction of the medial retinaculum and patellar ligament complex with realignment of the patella (based on clinical findings of a palpable defect and tendency to re-dislocate, and re-fixation of osteochondral fragments). Osteochondral or chondral fragments were verified by MRI or radiographic findings in 29% of all patients. The overall re-dislocation rate was 26% across all groups where the group with osteochondral re-fixation had the highest rate (33%) and simple arthroscopy had the lowest (20%). If, however, the primary dislocation occurred in children younger than age 15 years, their re-dislocation rate was 52%. Women were also more likely to re-dislocate than men. Thirty-nine percent of the patients with a re-dislocation required another operation. The largest group came from conservative therapy. Proximal soft tissue realignment and medial tuberosity transfer were the two procedures performed. No significant differences between activity level, function, pain, and subjective evaluation were noticed. Eighty-five percent reported excellent or good Lysholm scores and 71% reported good subjective results. The authors did not find any significant difference in results between patients with and without redislocation. Based on the results, the authors still recommend conservative treatment as the first option assuming the criteria to operate mentioned above do not apply.
Osteochondral defects Patellar dislocation not only results in soft-tissue injury, but may also present with osteochondral defects due to the high-impact force of the medial aspect of the patella hitting the lateral femoral condyle on dislocation. Nomura et al. [10] studied 39 knees to evaluate the frequency and pathology of osteochondral injury upon acute lateral patellar dislocation. All patients were below the age of 40 years, and patients with patellar cartilage damage due to a direct blow were excluded. Thirty-seven of the knees showed articular cartilage injury of the patella upon arthroscopic examination. In addition, 12 knees demonstrated cartilage injury of the lateral femoral condyle at the lateral margin of the weight-bearing surface or lateral end of the sulcus terminalis. Seventy-two percent of the knees had a cartilage defect of the patella with 64% occurring at the medial facet and 25% affecting the medial facet and central dome. No defects were present on the lateral facet of the patella, but 10% showed cracks. Thirty knees (77%) showed cracks in the patella with half occurring at the central dome and 27% occurring at the central dome and medial facet. The authors did not present outcomes or course of treatment regarding this study.
Proximal and distal realignment procedures When nonoperative care fails to improve patellofemoral stability, many surgical options are available. Proximal
realignment surgery involving the soft-tissue structures of the knee is performed to either tighten the medial side (medial reefing, VMO advancement, MPFL repair or reconstruction) or loosen the lateral side (lateral release). These procedures can be performed open or arthroscopically. Distal realignment surgery moves the tibial tubercle with the patellar tendon to improve tracking of the patella. Often both of these procedures are performed to improve patellar instability.
Proximal realignment Nam and Karzel [11] retrospectively reviewed mini-open medial reefing and arthroscopic lateral release in the treatment of recurrent patellar dislocation. This study included 22 patients with an average follow-up of 4.4 years. Patients incurred their first dislocation at an average age of 15 years and underwent surgery at an average age of 23 years. Inclusion criteria was positive apprehension at 308 of flexion and 3þ or higher lateral glide under anesthesia. The average Q-angle at extension was 158 and 5.78 when measured at 908 of flexion. Adequate lateral release was determined by improved medial glide and the ability to passively evert the patella. After advancing the medial retinaculum, motion and stability were assessed to ensure 908 flexion by adjusting suture tension and congruent tracking by visual confirmation of the patella centralized in the trochlear groove. Surgical findings showed that 74% of patients had osteochondral defects. Patient Tegner activity level score improved postoperatively with a mean Kujala score of 88.2 13.5. Ninety-one percent of patients’ subjective scores were good or excellent with no poor outcomes. Two patients had recurrent instability; distal tibial tubercle realignment was suggested to the skeletally mature individual. Regarding complications, three patients had a flexion loss. The patient with the greatest flexion loss demonstrated a range of motion from 0 to 708. One patient was treated with manipulation under anesthesia. Two patients had arthroscopic lysis of adhesions and a repeat lateral release. Nearly half the study population showed patella alta or trochlear dysplasia, but only two patients suffered recurrent problems after this proximal surgery that did not address their anatomic abnormality. The MPFL and VMO were not restored to their normal anatomic positions. Woods et al. [12] performed a prospective cohort study in which the distal aspect of the vastus lateralis tendon was released in recurrent dislocators (three or more episodes of instability with at least one confirmed dislocation) with no previous surgical intervention. This procedure was performed on 20 patients: 14 female (average age 19 years) and six male (average age 28.2 years). All participants had decreased levels of activity on presentation. The procedure involved arthroscopically releasing the vastus lateralis tendon from its insertion at the superior
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pole of the patella to a distance 2.0–2.5 cm proximally along the lateral border of the quadriceps tendon. Postoperatively, the patients were to bear weight as tolerated and participate in 4 weeks of rehabilitation. Average follow-up was 27 months during which no patient redislocated, received additional surgery, and none had neither subjective nor clinical signs of medial patellar instability. Postoperatively mean quadriceps strength improved an average 28%. Nineteen of the patients improved on their International Knee Documentation Committee and Short Form-36 scores.
Medial patellofemoral ligament repair and reconstruction The MPFL is the primary static checkrein to lateral displacement of the patella, and is a part of the medial patellofemoral retinaculum (MPFR). Thus, failure of the ligament increases the likelihood of patellar dislocation. With MPFL rupture occurring at 26 mm and patellar dislocation generally requiring 50 mm of patellar displacement, the MPFL must tear in order for the patella to displace laterally [13]. Smirk and Morris [14] performed a study to further define the anatomy of the MPFL and to assess the best site of attachment for the graft. Four cadaver knees were used to determine the site of graft attachment through a flexion range of 0–1208. Points were considered isometric if there was 5 mm or less elongation. Their results showed that the MPFL spans from the posterior medial epicondyle to the superomedial patella. It also attaches to the underside of the vastus medialis and quadriceps tendon. The most important points of MPFL attachment were the superior patella and posterior and inferior to the adductor tubercle. Mountney et al. [13] performed a cadaver study to analyze the stability of different fixation methods of the MPFL at its patellar attachment. Using 10 fresh cadavers without a history of patellofemoral instability, the MPFL was dissected out and left intact at its femoral attachment. Q-angle, patella alta, or trochlear dysplasia were not recorded. The patellar attachment was created using several methods: Kessler suture technique or reconstructed with bone anchors or one of two grafting techniques. Of the fixation techniques, through-tunnel tendon reconstruction failed at 195 N, which was not significantly different than the normal failure force of the MPFL. This procedure involved a tunnel drilled along the epicondylar axis of the femur with the bovine extensor tendon graft anchored by a titanium soft-tissue screw on the lateral side of the femur. A second tunnel was drilled from the medial to lateral side of the patella with the graft anchored on the lateral side of the patella by a titanium soft-tissue screw. Sutures failed most readily at a mean force of 37 N. Repair with sutures
occurred using the standard Kessler-suture method. The suture anchors plus sutures method failed with a mean force of 142 N. This method involved biodegradable corkscrew bone anchors with sutures to be placed into the medial femoral epicondyle and medial border of the patella and tied together. The authors recommended the bone anchor method as it was less intrusive and uses biodegradable products while maintaining a restraining force similar to the natural MPFL. Limitations of this experiment were the use of elderly cadaveric specimens. Thus, the viability of the medial epicondyle was not ideal due to the thin cortex of the bone that would not be commonly seen in younger patients. Gomes et al. [15] performed a prospective nonrandomized study with 15 patients (16 knees) with chronic patellar instability that underwent MPFL reconstruction with semitendinosus autograft. The average patient age was 26.7 years and there were 11 women and four men. All dislocations were nontraumatic. Exclusion criteria included a Q angle over 208 and valgus over 108. Patients with ligamentous laxity, patella alta and trochlear dysplasia were not excluded from the study. The minimum follow up was 5 years. During the surgical procedure, the semitendinosus autograft was attached at 608 of flexion to account for the flexibility of the tendon. They evaluated outcome using the Crosby–Insall and Angletti protocols. Using the Crosby–Insall criteria 11 knees were excellent, four good, and one poor. Using the Angletti protocol 11 knees were excellent, three good, one fair, and one poor. Patellar tracking was considered normal in 14 knees, and slightly altered in one. One knee required a second procedure; a fibrous bridge reuniting the lateral retinaculum was cut down and an anteromedialization procedure was performed. Patellofemoral pain was absent and the apprehension test negative in 15 knees. Sixty percent of the patients resumed physical activity and five patients began physical activity after the procedure. Cossey and Patterson [16] retrospectively reviewed a surgical procedure to treat patellar instability. Eighteen patients who failed conservative therapy and had chronic patellofemoral instability were followed for an average of 2 years postoperatively. They underwent a lateral release, distal realignment of the tibial tubercle and anatomic reconstruction of the MPFL using a graft composed of a redundant strip of medial retinacular tissue. Results showed no signs of instability and significant return to predislocation activity. Also, graft donor site morbidity was low and patient outcome scores, especially objective stability of the patella to lateral shift, were excellent. A retrospective study [17] looked at the outcome of patients with trochlear dysplasia undergoing medial patellofemoral reconstruction to treat their chronic patellar instability. Thirty-four patients, 22 female (average
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Patellofemoral instability Merchant and Bennett 157
age 25 years) and 12 male (average age 31 years) were included in this study. They were divided into three groups based on their preoperative symptoms. Group A had documented patellar dislocations, group B reported subjective patellar subluxation, and group C reported pain without subluxation or dislocation history. All patients had trochlear dysplasia based on lateral knee radiographs. Patients were not excluded based on previous surgical history. For the surgical procedure three different grafts were used to reconstruct the MPFL: adductor magnus tendon autograft, quadriceps tendon autograft, and patellar tendon allograft. All grafts were placed in an isometric position on the medial epicondyle. Mean follow-up was at 66.5 months (range, 24–130 months). Kujala, Tegner, and Lysholm scores all improved (P < 0.001). There was no statistical difference in knee scores based on the above tests when comparing degree of dysplasia, graft type, or degree of symptoms. No recurrent dislocations occurred during the follow-up period. The authors concluded that MPFL reconstruction in patients with trochlear dysplasia benefits from long-term pain relief and functional return.
Medial patellofemoral ligament reconstruction in children Proximal surgery is preferred in skeletally immature patients as it avoids the tibial epiphyseal plates. Thus, it is safer to fix the MPFL in children if that may improve their instability instead of performing a distal realignment. A second procedure can be performed to correct their anatomical predisposition once their plates have fused. Deie et al. [18] reconstructed the MPFL to treat recurrent patellar dislocation in children. Six knees were used in the study with follow-up for a minimum of 4 years. The mean age of the patients was 8.5 years. All the patients had patella alta, contracture of the lateral patellar tissues, and hypoplasia of the lateral femoral condyle. Reconstruction of the MPFL was performed using the semitendinosus tendon, which was divided in half at its musculotendinous junction and separated leaving the distal attachment intact. An incision was made in the posterior portion of the medial collateral ligament (MCL) at its femoral attachment to serve as a pulley for the free end of the MPFL graft. This end is then sutured to the surface of the patella with the knee flexed at 308. No redislocations were noticed after surgery. All knees had full range of motion. The mean Kujala score was 96.3. One girl maintained positive apprehension in both her knees after surgery. Disadvantages of this procedure posed by the author are the inferior force applied to the patella by the graft and the lack of isometricity to the graft. Patella alta and hypermobility of the patella is not corrected by this procedure.
Distal realignment: Elmslie–Trillat The Elmslie–Trillat procedure is used to treat patients with chronic or habitual patellar dislocations by moving the tibial tubercle medially without distal displacement, lateral release, and medial reefing. Over the long term, the results of this procedure are relatively constant. Redislocation is minimal, but functional scores tend to decrease over time [19,20]. To improve immediate results, an additional step can be added to improve stability [21]. Marcacci et al. [21] performed a modified version of the Elmslie–Trillat procedure in patients who demonstrated continued dynamic instability of the patella after tibial tuberosity transfer. The modification was the use of the medial third of the patellar tendon to help further stabilize the patella. A 1 cm long and 0.5 cm wide bone plug from the medialized tibial tuberosity along with the medial third of the patellar tendon is separated and positioned medially and posteriorly under tension to stabilize the joint based on dynamic function. Eighteen knees were used in the study, each of which demonstrated subluxation or dislocation on dynamic testing during surgery. Functional deficit, retropatellar tenderness, and crepitus were the main complaint of the habitual dislocators before surgery. All patients presented with patella alta and grade II or worse trochlear dysplasia radiographically based on Insall–Salvati criteria. This modified technique indirectly improved patella alta in all patients. Four knees underwent simultaneous deepening trochleoplasty, and they were evaluated as part of the group and individually. The four patients who underwent trochleoplasty did not fair as well as the patients who did not undergo this procedure. Using the Kujala score, 89% of the knees showed excellent results at follow-up (average of 5 years) without any report of patellar dislocation since the surgical procedure. Two knees were not excellent; the fair case showed some retropatellar tenderness and the poor case resulted from overcorrection of the congruence angle and preoperative degenerative changes. There were no further degenerative changes noticed on radiographic imaging at followup compared to preoperatively. All patients showing excellent results regained full ROM and could perform strenuous activity without discomfort. Carney et al. [20] examined the long-term outcome of the Elmslie–Trillat procedure for recurrent patellar dislocation by following 18 patients for an average of 26 years. These patients were selected from a study group that was originally followed for 3 years. There was no difference in the rate of re-dislocation within the patient group between the 3-year and 26-year follow-up. Three years out from surgery, however, 73% rated their knee as excellent, but only 54% rated their knees as excellent at 26 years follow-up. It is important to note that MRI and
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arthroscopy were not available when these patients were first evaluated, so it is possible that they had osteochondral lesions that were not discovered. This study was performed without a control group and with a predominantly young male study group. The authors also did not evaluate patellar height or ligamentous laxity in the patients. A study [22] used cadaveric human knees to compare the effects of medializing and anteromedializing the tibial tubercle during procedures to correct patellar instability in adults. The testing range was 0–908 of flexion when collecting patellofemoral joint contact pressures and kinematic data. Within this flexion range, they tested four scenarios: normal knee, increased Q-angle, postmedialization of the tibial tubercle, and postanteromedialization of the tubercle. Their results demonstrated that both procedures improved abnormal contact pressures and patella maltracking. Medialization improved the shift of force to the lateral facet created by an increased Q-angle, however, whereas anteromedialization did not.
Modified Roux–Goldthwait A retrospective study [23] reviewed 30 knees (20 patients) in a pediatric population (average age 14.2 years) with chronic patellar instability that were treated with a modified Roux–Goldthwait technique including the release of contracted structures. The modification in the procedure is a longitudinal incision that is made in the patellar tendon separating the lateral half of the tendon and detaching it distally at the tibial tubercle. This portion is then moved distally and reattached underneath the medial half of the patellar tendon. Average follow-up was 6.2 years. The procedure demonstrated excellent (26) and good (three) results in 29 knees. All patients showed an improvement in leg strength of 80% or greater.
Trochleoplasty Another retrospective study [24] looked at 45 knees in 38 patients (22 female and 16 male) with a mean followup of 8.3 years (range, 4–14 years). The average age of the patients was 22 years. Thirty-three percent of the knees had undergone previous patellar procedures such as debridement, medial reefing, lateral release, or medial tibial tuberosity transfer. The trochleoplasty was performed by chiseling off the distal, anterior, medial and lateral femoral condyles with the trochlea as one osteochondral section. The subchondral groove was then deepened and the osteochondral piece was re-seated in the new groove. Proximal realignment procedures were also performed as needed. The results demonstrated no re-dislocations, but in one-third of the patients patellofemoral pain worsened after the procedure. Radiographically, 94% of the patients demonstrated a correction of the dysplasia, but degenerative
changes were present in 30% of the knees. The authors concluded that the procedure treated the recurrent dislocation, but its effects on pain and degenerative changes were unpredictable.
Prophylactic surgery An area of focus for patellar instability treatment has been correcting anatomical abnormalities in patients that appear predisposed to dislocation based on clinical and radiographic findings. Palmer et al. [25] performed a surgical procedure that aims to correct all abnormalities of patellofemoral maltracking by performing proximal and distal realignment: a lateral release, VMO advancement, and tibial tubercle transfer. Eighty-four patients and 107 knees were used in the study in which 55% suffered from a recurrent dislocation and the remaining patients complained of anterior knee pain with clinically abnormal tracking of the patella (no history of subluxation/dislocation). Medial shift (5–10 mm) of the tibial tubercle was performed to improve the Q-angle. Distal movement decreased patella alta (by placing the distal pole of the patella 10 mm superior to the tibial plateau). In patients with retropatellar degeneration, the tibial tubercle was moved anteriorly to improve tracking and decrease pain. VMO advancement and tensioning was performed at 458 flexion and the muscle was positioned distally and laterally over the front of the patella. The average age of the patients was 30 years with 51 women and 33 men as the patient population. All patients had failed conservative therapy and 15% had failed previous patellofemoral realignment procedures. Seventy-eight percent had patella alta. Average follow-up for the patients was 5.6 years. These results did not vary between the two study groups significantly. Eighty percent of the patients with dislocation and 71% of the patients with anterior knee pain had a good to excellent functional outcome. Patients who presented with patellofemoral degeneration, radiographic or gross evidence, did as well as those patients who did not have any damage. Patients undergoing this procedure, however, also demonstrated a significant increase in patellofemoral degeneration upon radiographic study at follow-up. During follow-up, approximately 25% of patients presented with either effusion, positive apprehension, or some maltracking. Patients also showed an average flexion deficit of 48 and 13% had a deficit of 108. Six patients required manipulation under anesthesia. Five patients were worse after surgery than preoperatively based on the Crosby and Insall rating due to their persistent anterior knee pain; their instability had been resolved. Two patients had recurrent dislocations, which correlated with their significant generalized ligamentous laxity. It is unknown to which group they belonged. Six patients showed recurrent subluxation. Fifteen patients required removal of metalwork from the tibial tubercle transfer due to consistent pain.
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Patellofemoral instability Merchant and Bennett 159
Diks et al. [26] performed a study comparing the outcomes of patients with a maltracking patella versus patients with a subluxation/dislocation history and anatomical abnormalities undergoing computed tomography (CT)-guided tuberosity transfer. Patients with a lateral tracking patella had no history of instability, only pain. Forty-three knees were evaluated, with an average patient age of 25 years. They were divided into the lateral tracking patella (n ¼ 16) and objective patellar instability (n ¼ 27). Seventy-eight percent of the dislocation group showed trochlear dysplasia and patella alta. The distance between the tibial tuberosity and trochlear groove (TTTG) was increased in 93% of patients in the dislocation group. In the maltracking group, however, only 25% had trochlear dysplasia, 44% had patella alta, and 100% had pathological lateralization of the TTTG. Most knees underwent a medialization of the tuberosity of 3–12 mm that resulted in the tuberosity sitting 10– 12 mm laterally of the trochlear groove with the knee at 908. This process was checked by calculations made prior to surgery using CT images. Twenty-eight knees also underwent a distalization procedure of 3–20 mm to account for patella alta. Follow-up was 25–55 months. Results showed that 63% of the dislocation group had excellent to good results and nine patients (33%) had a fair result. This rating was determined by full sports participation, only slight pain with extreme activity, full range of motion and no instability. Only one patient had recurrent instability; thus, 96% had an improvement in stability and only 63% had an improvement in pain. Maltracking patella patients showed 81% of patients with excellent (n ¼ 6) and good (n ¼ 7) results. Only three (19%) patients had fair results and no one had a poor result. Based on the results patients with a lateral tracking patella were 2.6 times more likely to have an improvement in pain after surgery compared to patients with a history of dislocation. This procedure showed improvement in stability in many patients with trochlear dysplasia. The authors advise separating patients with a maltracking patella as the cause of their generalized patellofemoral pain since surgical treatment appears to improve their symptoms.
Conclusion Patellar stability depends on multiple factors. The integrity of the soft tissues surrounding the joint, bony anatomy of the knee, and the motion of the patella all influence whether dislocation may occur. From the findings above, patellar stability is lowest at 208 of flexion [1], and thus, more likely to dislocate at this angle [4]. In the event of a primary, acute dislocation nonoperative therapy remains the norm [9]. The previously held notion of strengthening the VMO during rehabilitation, however, appears to be less effective in improving stability surrounding the patella [1]. Operative treatment for patients with recurrent instability is more popular.
Lateral release is increasingly performed arthroscopically in conjunction with other proximal realignment procedures and with good results; though, MPFL and VMO damage and anatomical abnormalities cannot be corrected [11]. MPFL reconstruction shows good results with semitendinosus and medial retinacular tissue choices as grafts in adults and children [15,16,18]. Elmslie–Trillat procedures demonstrate longevity in guarding against instability [20]. For the cases in which instability remains, the modifications demonstrated by Marcacci et al. should improve stability [21]. Aside from performing surgery after instability exists, positive results from treating patients with pain and a maltracking patella in the absence of gross instability are also promising [25,26].
References and recommended reading Papers of particular interest, published within the annual period of review, have been highlighted as: of special interest of outstanding interest Additional references related to this topic can also be found in the Current World Literature section in this issue (p. 199). 1
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Brunet ME, Brinker MR, Mark R, et al. Patellar tracking during simulated quadriceps contraction. Clin Orthop 2003; 414:266–275.
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Fithian DC, Paxton EW, Stone ML, Silva P, et al. Epidemiology and natural history of acute patellar dislocation. Am J Sports Med 2004; 32:1114– 1121.
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Elias JJ, Cech JA, Weinstein DM, Cosgrea AJ. Reducing the lateral force acting on the patella does not consistently decrease patellofemoral pressures. Am J Sports Med 2004; 32:1202–1208.
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