Abstract
Background:
The medial patellomeniscal ligament has been determined in vitro to be the only substantial distal-medial restraint to lateral patellar displacement. The purpose of this study of prospectively collected data was to determine if isolated deficiency of the medial patellomeniscal ligament, resulting in excessive lateral patellar translation and associated symptoms, could be identified. We hypothesized that, if symptoms were associated with isolated deficiency of that ligament, the laxity and symptoms should resolve after plication of that ligament alone.
Methods:
Testing for lateral patellar displacement in the extended knee by exertion of force through the distal patellar attachment of the medial patellomeniscal ligament was performed on 745 patients with patellofemoral syndromes during a twenty-eight-month period. In addition, the ability to recognize pathologically increased lateral patellar translation preoperatively with use of such testing was compared with the ability to recognize increased lateral translation with testing in 439 patients undergoing arthroscopy under anesthesia during that period for any reason. Preoperative symptoms and impairment in knees with isolated deficiency of the medial patellomeniscal ligament were documented and compared with the postoperative results.
Results:
Isolated medial patellomeniscal ligament deficiency was identified with testing under anesthesia in twenty-three of the 439 knees undergoing arthroscopy for any reason, and twenty of those twenty-three cases had been detected preoperatively with use of lateral patellar displacement testing. Isolated medial patellomeniscal ligament plication was performed in these twenty-three cases, and follow-up data at a mean of 30.8 months were available for twenty-one of the cases. The mean International Knee Documentation Committee subjective score increased from 38.9 preoperatively to 84.6 postoperatively, and recurrent symptomatic pathological lateral patellar translation was present in only one patient.
Conclusions:
Isolated deficiency of the medial patellomeniscal ligament can be detected by physical examination. Restoration of the normal length of the ligament by plication can lead to resolution of detectable patellar subluxation and its associated symptoms.
Level of Evidence:
Diagnostic Level IV. See Instructions to Authors for a complete description of levels of evidence.
In vitro studies have confirmed the medial patellomeniscal ligament (MPML) to be the only substantial distal-medial soft-tissue restraint to lateral patellar displacement1-6. The MPML, located in layer 3 of the medial portion of the knee7, attaches to the inferomedial aspect of the patella and extends obliquely, medially, and inferiorly within the medial portion of the fat pad. It attaches to the medial meniscus anterior to the medial collateral ligament, and to the tibia through the coronary ligaments1 (Fig. 1). During active terminal knee extension, these medial patellar and tibial attachments create a distal-medial resultant force vector that may serve to balance the lateral resultant force vector created by the lateral tibial insertion of the patellar tendon (Fig. 2).
Nevertheless, the role of the MPML in clinically evident patellofemoral instability has been largely ignored, while interest has been almost exclusively directed toward the proximal restraint, the medial patellofemoral ligament (MPFL)8-13. The physical examination technique for establishing competence or deficiency of the MPFL has been previously reported14. Sequential repair of the MPFL and the MPML15 has allowed the senior author (W.P.G. Jr.) to gain surgical experience with the subtleties involved in detecting patellofemoral laxity in the extended knee following plication of the MPFL and prior to plication of the MPML. A laxity resulting in translation by more than 50% of the width of the patella, which has previously been described as pathological16, was used to define subluxation in this report. We have previously noted that in vivo, following MPFL repair, plication of the MPML leads to resolution of residual subluxation15. The senior author has also demonstrated patellar subluxation in the extended knee in vitro after cutting only the MPML while leaving the MPFL intact. We questioned whether this excessive lateral patellar translation in knees with an intact MPFL, demonstrated only at terminal knee extension, was present in patients presenting to us with knee symptoms.
What we have not known is whether demonstrable patellar subluxation in the fully extended knee (0° to 10° of flexion) that resolves with plication of a lax MPML is clinically important in cases in which we are confident that the MPFL-vastus medialis obliquus complex is intact. To demonstrate a clinically important syndrome of isolated MPML deficiency, in the presence of an intact MPFL, it is necessary to show that lateral patellar subluxation at terminal knee extension is associated with symptoms consistent with episodic subluxation and/or maltracking. Furthermore, demonstrable patellar subluxation at terminal knee extension and associated symptoms must resolve following isolated repair of the MPML.
The purpose of this study was to identify whether a lax MPML in the presence of an intact MPFL can be detected and whether that detectable subluxation is associated with a clinically important syndrome consistent with increased lateral translation of the patella in the extended knee. We report the physical examination technique that we used for recognizing isolated deficiency of the MPML, which was confirmed by arthroscopic documentation of demonstrable patellar subluxation in terminal knee extension and which resolved after isolated repair of the MPML. In order to rule out or confirm isolated MPML deficiency as a clinically important entity, the effectiveness of MPML plication in correcting demonstrable subluxation and associated symptoms was also evaluated. Plication of the lax MPML was performed in a nonrandomized study of cases in which conservative treatment had failed. The success of the plication in correcting demonstrable subluxation and associated knee extensor dysfunction after a mean duration of follow-up exceeding two years is reported.
Our institutional review board granted approval for a retrospective review of data collected prospectively in two cohort groups. Group 1 included patients presenting with anterior knee pain and/or patellar instability between February 2001 and May 2003. Group 2 included all patients undergoing knee arthroscopy for any reason during that period.
The preoperative and postoperative symptoms, activity level (on a scale of 1 to 5), and overall function (on a scale of 0 to 10) in each knee undergoing MPML plication were assessed by one of the authors (L.F.) with use of the 2000 version of the International Knee Documentation Committee (IKDC) subjective knee form17. This form is a validated questionnaire that includes the assessment of activity level and knee function, including giving-way, activity-related pain and swelling, jumping using the involved leg, pivoting, squatting, using stairs, quickly stopping and starting, and rising from a sitting position in which the knee is bent. The maximum possible total score is 100 points, indicating the highest level of function without symptoms.
All patients evaluated in the physician's office for knee symptoms who were to undergo knee arthroscopy during the study period underwent an examination to look for increased lateral patellar translation. During this patellofemoral evaluation, the examiner sought to identify and record tenderness and/or increased lateral patellar translation while specifically examining the MPML and the MPFL. MPFL integrity was tested as previously described5,6,14 (Fig. 3-A). In the presence of an intact MPFL, isolated deficiency of the MPML was identified when subluxation, defined as increased lateral translation of the patella with uncovering of the entire medial aspect of the femoral trochlea as palpated by the examiner, was detected when force was applied to the attachment site of the MPML on the distal-medial aspect of the patella in a lateral and slightly proximal direction with the knee in 0° to 10° of flexion (Fig. 3-B).
Laxity of the distal-medial restraint was determined by comparison with the contralateral, asymptomatic knee as the examiner sat in front of the patient, with the patient's feet on the examiner's lap, the quadriceps relaxed, and the knees in nearly full extension. Both patellae were examined simultaneously, with the examiner attempting to apply equal forces (Figs. 3-A and 3-B). A lax MPML was identified on the basis of a soft end point to displacement and excessive translation of the patella relative to that in the asymptomatic knee. Translation was judged to be abnormal and excessive when the uncovered medial one-half of the femoral trochlea could be palpated. The medial condyle of the trochlea typically remained covered and could not be palpated on the contralateral, asymptomatic, morphologically identical knee, which served as a control for this physical finding. In each case, external validation of the difference in physical findings between the symptomatic and the asymptomatic knee was provided both by the patient's acknowledgment of the difference and by a second examiner. Subsequently, arthroscopy allowed visual confirmation of the patellar subluxation in terminal knee extension when the deficient MPML was tested as well as the lack of subluxation during MPFL testing as described previously (Figs. 4-A and 4-B).
The knee was evaluated for excessive tautness of the lateral retinaculum (the Sage sign)16,18 and lateral patellofemoral tenderness. The Q angle was measured and recorded at full extension with the quadriceps relaxed and the patella centered in the trochlea, ensuring that the lateral aspect of the patella did not overhang the lateral margin of the femoral trochlea.
These preoperative and intraoperative examinations were all performed by the senior author (W.P.G. Jr.), who also performed each surgical tensioning of a lax MPML. The preoperative results of the lateral patellar displacement testing were compared with the results of displacement testing performed with the patient under anesthesia, as visualized through anterolateral and anteromedial portals during arthroscopic examination19. All patients in Group 2 had testing of the MPFL and MPML performed preoperatively and intraoperatively as described below. The patients underwent objective assessments including measurement of the Q angle; isotonic lower-extremity strength evaluation; anteroposterior, lateral, and bilateral Merchant view radiographs; and arthroscopic documentation of patellar subluxation. The radiographs were used to evaluate the sulcus angle, patellar tilt, and the presence of patella alta (with use of the Insall-Salvati ratio of the length of the patellar tendon to that of the patella20) and patellar subluxation (as determined by the patellofemoral congruence angle21).
Final follow-up examination of patients who had undergone MPML repair was performed by the senior author, and an independent physical examination was performed by the second physician author (G.S.C.). The examiners were not blinded with regard to the operatively treated knee. Findings on the physical examination performed during the follow-up visit were recorded independently by the senior author and the second physician author and were subsequently checked for agreement.
All patients presenting with anterior knee pain, giving-way, or episodic patellar subluxation or dislocation underwent a trial of conservative management involving nonsteroidal anti-inflammatory medications, bracing with a laterally padded neoprene knee sleeve, and initiation of a rehabilitative exercise program22. Arch supports with a medial heel wedge were utilized by patients with pes planus. Rehabilitative exercises were directed toward strengthening the knee extensor mechanism while avoiding aggravation of pain. Patients with MPML deficiency performed closed-kinetic-chain knee extension exercises. Open-chain, terminal knee extension, progressive resistance exercises aggravated pain in a subset of the patients with a lax MPML and were avoided. If, after a minimum of eight weeks of rest and rehabilitation, symptoms were not sufficiently decreased (IKDC score, <70) and the patient continued to have detectable increased lateral patellar translation during testing of the MPML (demonstrated patellar subluxation), operative intervention was considered. Four patients who presented with combined anterior cruciate ligament (ACL) deficiency and MPML laxity with pain and apprehension underwent ACL reconstruction after a delay of eight weeks in an attempt to allow resolution of the MPML laxity.
Surgical Technique
The patient was placed in a supine position and physical examination was performed on both the injured and the uninjured extremity, with the patient under anesthesia, to confirm the preoperative physical findings. Each symptomatic knee underwent arthroscopic evaluation to identify any concomitant intra-articular pathology as well as to visualize patellar tracking and/or lateral subluxation during manual testing of the MPFL or MPML (Figs. 4-A and 4-B).
In cases of MPML laxity, a laterally and slightly proximally directed force on the inferomedial patellar attachment of the MPML at terminal knee extension resulted in subluxation of the patella, which could be visualized and was defined by the uncovering of the entire medial femoral trochlea (Figs. 4-A and 4-B) and lateral displacement of the central ridge of the patella over the lateral margin of the femoral sulcus. In cases of isolated MPML laxity, the results of displacement testing for a lax MPFL were negative.
In the open procedure, an oblique 3-cm incision was made approximately 1 cm from and parallel to the inferomedial margin of the patella. Dissection was performed to identify the soft-tissue layers, including subcutaneous fat, the superficial fascia, and layers 1 and 2, which blend anteriorly with layer 37. The MPML in layer 3 was identified by placing tension on the proximal-medial portion of the fat pad in the direction extending from the medial joint line (anterior to the medial collateral ligament) toward the inferomedial border of the patella. The MPML fibers in the medial portion of the fat pad run deep to the tissue previously described as the patellar tibial ligament7. Excision of ≤1 cm of the lax MPML was performed at the proximal edge of the ligament fibers adjacent to the inferomedial border of the patella. The remaining MPML was then advanced proximally and laterally to the periosteal tissue at the inferomedial border of the patella with use of number-1-0 polydioxanone (PDS) sutures. Following the tying of the sutures and before closure of capsular layers 1 and 2, the ability to subluxate the patella was noted to have been corrected in all cases. Incisions were closed with subcutaneous 2-0 Vicryl (polyglactin; Ethicon, Somerville, New Jersey) and a running subcuticular 4-0 PDS suture.
In later cases, an arthroscopic technique was utilized to repair the MPML. After arthroscopic evaluation confirmed that pathologically increased lateral patellar translation occurred only during stressing of the MPML, attention was turned to the inferomedial border of the patella. Following debridement of ≤1 cm of fatty tissue in the gutter adjacent to the inferomedial aspect of the patella, suture passers (Meniscus Mender II Outside-In Meniscal Repair System; Smith & Nephew, Andover, Massachusetts) were used to pass a 1-0 PDS suture at the inferomedial periosteal border of the patella and deliver it into the joint under arthroscopic visualization. A second suture passer needle was inserted through the skin and soft tissue including the MPML approximately 1.5 cm distal and medial to the initially placed needle. After the suture was passed with use of this initial needle placement, a second set of needles was inserted parallel to the initial set and approximately 1 to 1.5 cm more proximally, near the most proximal margin of the MPML. A 10-mm incision was then made through the skin and subcutaneous tissue between the entrance and exit sites of each respective suture. An extracapsular tract was created by a hemostat, deep to the subcutaneous tissue, through each incision to the site at which the sutures exited from the knee capsule. The hemostat was used to grasp the proximal-lateral and distal-medial limbs of the sutures and pull them through the tract to exit the incision. The sutures were then sequentially tied tightly, effectively plicating the MPML and the overlying superficial retinacular tissue. The portal wounds were closed with use of 3-0 nylon sutures.
In both open and arthroscopically performed operations, advancing the MPML approximately 1 cm prevented the pathological displacement of the central patellar ridge over the lateral trochlear margin without excessively restraining the patella. Following MPML plication, the patella could be displaced laterally approximately one-fourth of its width in the extended knee position. Normal patellar tracking was visualized arthroscopically following plication, with the patella resting slightly laterally in full knee extension but gaining full contact with the medial aspect of the trochlea by 55° of knee flexion5,18.
Postoperative Rehabilitation
Patients were encouraged to perform active quadriceps setting, straight leg raising, and range-of-motion exercises as tolerated, beginning on the first postoperative day. As soon as straight leg raising without an extensor lag was exhibited, full weight-bearing was encouraged. A long-leg hinged knee brace, allowing range of motion as demonstrated actively by the patient, was utilized until good quadriceps control over a 120° range of motion was documented. Following these range-of-motion milestones, use of the brace was discontinued, typically within three weeks postoperatively. This strengthening protocol was similar to the preoperative regimen. Full activity including running was allowed when leg-press strength and knee-extension strength reached 80% of those of the contralateral limb, typically by three months postoperatively in patients not limited by comorbidities.
Statistical Analysis
The chi-square test was used to determine if there was a >50% chance that the Q angle was >20°. The one-sided null hypothesis that, in patients with MPML deficiency, the sulcus angle exceeded 125° (within one standard deviation of the mean for the general population, in which the sulcus angle is 135° ± 9°21) was analyzed with a single-sample t test. The null hypothesis that knee pathology in addition to the lax MPML was not present in cases with a poorer result was analyzed with use of a paired t test. Multiple regression analysis was used to evaluate whether age was a significant confounder. The relationship between sex and the IKDC subjective results was analyzed with use of a paired t test.
Source of Funding
There was no external source of funding for this study.
During the study period, 745 patients (Group 1) were seen for anterior knee pain and/or giving-way attributed to knee extensor dysfunction. Arthroscopy was performed on the knees of seventy-three of these patients because of symptoms associated with patellar maltracking and/or instability. The specific surgical procedures performed for these seventy-three cases to address specific pathological conditions indicated by the physical examination findings are presented in a table in the Appendix; 32% required isolated MPML plication. Including the seventy-three knees with patellar maltracking and/or instability, a total of 439 knees (Group 2) underwent arthroscopy for any reason during the study period, and a patellofemoral stability examination was performed on all of these knees.
Thirty (4%) of the 745 consecutive patients with anterior knee pain and/or giving-way had MPML deficiency and an intact MPFL. Seventeen of the thirty were female and thirteen were male; the mean age was 18.6 years (range, eleven to thirty-four years). The MPML injury was acute (identified less than two weeks after injury) in twenty-one patients, subacute (presenting two weeks to three months after injury) in seven, and chronic in two. Four of the thirty patients also had less severe patellofemoral symptoms and physical signs in the contralateral extremity. The Q angle, which was recorded preoperatively in twenty of the twenty-one knees available for follow-up, was 15° in four, 20° in three, 25° in eight, and 30° in five, with a mean of 23.5°. The chi-square test indicated a probability of ≥50% that the Q angle was >20° in patients in this subgroup (p = 0.05). The femoral sulcus angle, as determined radiographically, was symmetrical bilaterally in each patient, and ranged from 116° to 130°, with a mean (and standard deviation) of 125° ± 9°, compared with 135° ± 9° in the general population21. The single-sample t test rejected the one-sided null hypothesis that the sulcus angle tended to exceed 125° and thus fall within one standard deviation of the mean seen in the general population (p < 0.05). There were no cases of lateral patellar tilt21. No subluxation was noted at rest on the Merchant radiographic view preoperatively or postoperatively in any patient, as indicated by a normal patellofemoral congruence angle21. Lateral radiographs obtained at 30° of knee flexion revealed a mean Insall-Salvati ratio20 of 1.18 (range, 0.93 to 1.43). Ten knees with an Insall-Salvati ratio ranging from 1.18 to 1.43 had patella alta. No signs of trochlear dysplasia or trochlear bossing23,24 were observed on any of the lateral radiographs.
Twenty-three patients had persistent symptoms after an average of nine months of conservative treatment, and these patients opted for surgery. Pain and apprehension25 were reproduced with stressing of the MPML in each case. In twenty of the cases, pathologically increased lateral patellar translation that occurred only during stressing of the MPML was demonstrated preoperatively. In the remaining three knees, this demonstrable patellar subluxation was not fully appreciated until examination under anesthesia and arthroscopic visualization (Table I).
Ten of these twenty-three patients described overt episodes in which the patella popped out of place. (None reported a history of an obvious hemarthrosis typical of a traumatic dislocation.) All twenty-three patients had pain and giving-way during terminal knee extension while bearing weight. The mechanism of injury was described as a valgus, external-rotation twisting in three knees and as hyperextension in two; in the other cases, the mechanism was indeterminate. The injury or the onset of symptoms was sports-related (see Appendix) in twenty-one patients and due to a motor-vehicle collision in one; the cause was unknown for the remaining patient.
In all twenty-three patients, unilateral patellar subluxation was noted during MPML testing with the patient under anesthesia, when the patella was displaced laterally relative to the medial aspect of the femoral trochlea with the knee in 0° to 10° of flexion, and no subluxation was noted during MPFL testing. The subluxation was documented in each case by arthroscopic photography.
The operative group included six males and seventeen females (thirteen left knees and ten right knees). Because of the small sample size, a statistical analysis of the effect of sex was not meaningful.
Four patients (three with an acute injury) presented with ACL deficiency in addition to the deficiency of the MPML. In one of the patients with an acute injury, the increased lateral translation of the patella resolved during an eight-week rehabilitation period, and he underwent ACL reconstruction without MPML plication; that case is not included in the twenty-three surgically documented cases of MPML deficiency. The other three patients required MPML plication in addition to ACL reconstruction to correct persistent demonstrable subluxation of the patella and associated symptoms. Two of the patients undergoing ACL reconstruction also underwent lateral partial meniscectomies. Other associated procedures included four lateral meniscectomies in patients without an ACL tear. Three patients had chondral lesions of the trochlea, and three others had patellar chondral lesions (Table II).
A follow-up examination was performed for twenty-one of the twenty-three patients at a mean of 30.8 months (range, nineteen to eighty-four months) (see Appendix). The IKDC subjective score increased from a mean of 38.9 (range, 6 to 64) preoperatively to a mean of 84.6 (range, 56 to 100) postoperatively (Table II and Appendix). The postoperative IKDC score was >90 for ten patients, 81 to 90 for five, 71 to 80 for two, and <70 for four. All patients with a score of >80 returned to full athletic activity. Seven of eight patients without any other pathology and with lasting correction of demonstrable patellar subluxation had an IKDC score of 90 to 100, and the remaining patient had a score of 83. Thus, the null hypothesis that knee pathology in addition to the MPML laxity was not present in cases with a poorer result was rejected (Table II; p = 0.001). Because of the small number of cases, a statistical analysis of the effect of open compared with arthroscopic repair on the IKDC score was not meaningful.
The immediate elimination of the ability of the examiner to subluxate the patella following arthroscopic repair was documented in all cases. At the time of follow-up, a physical examination of each patient who had undergone MPML plication was performed independently by the surgeon and the second physician author. These examinations demonstrated that patellar subluxation had been eliminated by the MPML repair in twenty of the twenty-one patients. One failure of an arthroscopic ligament repair occurred within the first year (Case 9). That patient, a ballerina, had recurrence of symptoms and demonstrable subluxation, and she elected to have the arthroscopic repair repeated. At two years, she was doing well and was teaching ballet, without symptoms or recurrence of demonstrable subluxation, although she had not resumed vigorous ballet in order to reduce the risk of recurrence. No other patient had a recurrence of preoperative symptoms with an associated detectable subluxation. Isotonic strength testing performed at the one-year follow-up examination for the twenty-one patients revealed a mean strength equal to 98.1% of that of the contralateral limb on leg press, 92.4% on knee extension, and 98.3% on leg curl.
One patient sustained a cruciate ligament rupture resulting from a fall during the postoperative period and sought additional care at another hospital. This patient and one other (with a combined ACL and MPML deficiency) were lost to follow-up. There was one superficial wound infection, one patient underwent a second minor procedure to remove an uncomfortable subcutaneous suture, one patient required manipulation under anesthesia before obtaining a full range of motion, and another patient (Case 10) underwent a subsequent lateral retinacular release before having an optimal result. Twenty of the twenty-one patients available for follow-up had lasting stabilization of the patella and were able to return to their activities of choice, although one patient (Case 18) retired from volleyball after two years because of retropatellar pain, which we believe was related to a full-thickness chondral fissure in the central portion of the femoral trochlea noted at the time of MPML repair. Anecdotally, despite successful patellar stabilization, the poorer IKDC results, other than the one failure due to recurrent patellar instability (Case 9), were associated with a lateral meniscus tear and a valgus knee (Cases 16 and 17) and with a full-thickness chondral defect in the central portion of the femoral trochlea (Case 18).
This clinical study supports the thesis that a pathologically lax MPML, in the presence of an intact MPFL, may result in demonstrable lateral patellar subluxation at terminal knee extension. The excessive lateral translation exceeding 50% of the width of the patella16 may be associated with anterior knee pain, giving-way, and, in some cases, episodic transient patellar subluxation at terminal knee extension. Patellar subluxation can be demonstrated in these knees by applying a lateral displacement force to the patella through the inferomedial patellar attachment of the MPML with the knee in ≤10° of flexion. Patients with isolated MPML laxity may attempt to avoid discomfort by standing with the symptomatic knee slightly flexed or maintain a majority of their weight on the asymptomatic knee locked in full extension. This flexed-knee standing posture allows the patient to avoid pain that is aggravated by active terminal knee extension against resistance. On physical examination, pain that can be elicited as the examiner resists the patient's terminal knee extension is not elicited when resistance is applied to active extension from a position of 90° of knee flexion. Once the knee is flexed beyond 20°, progressive tension on an intact MPFL (normally lax in full knee extension) centers the patella in the trochlea5,12 and excessive lateral patellar translation cannot be demonstrated.
The sulcus angles in this series ranged from 116° to 130°, with a mean (and standard deviation) of 125° ± 9°. These relatively acute sulcus angles differ markedly from those in our previously reported series of athletes with combined MPFL and MPML laxity associated with overt traumatic patellar instability. In that series, the sulcus angle ranged from 135° to 153°, with a mean of 145°15 Patients with a more obtuse femoral sulcus angle appear to be unlikely to have an isolated MPML injury and therefore are probably poor candidates for isolated MPML repair. We hypothesize that the stabler patellofemoral configuration that occurs when the sulcus angle is relatively acute results in sufficient contact force to avoid excessive tension on the MPFL when it is stressed in knee flexion. However, the MPML in these knees remains vulnerable to injury in active terminal knee extension, when the MPFL is normally, physiologically lax and the patellofemoral contact force is less.
Previous in vitro biomechanical studies of lateral patellar displacement that simply named the MPFL as the primary and the MPML as the secondary medial soft-tissue restraint1-4 have probably oversimplified the role of these ligaments. To our knowledge, only one biomechanical study has been performed on the extended knee1, and in that study no tension was placed on the quadriceps to maintain the patella proximally in or above the trochlea, a position in which the MPML is under tension and the MPFL is relatively lax.
Patients with a unilaterally lax MPML tend to have a high Q angle, an acute sulcus angle, and, in almost half of the cases, patella alta. These morphological characteristics, which may tend to isolate and increase stress on the MPML, were symmetrical in the knees of our patients with unilateral symptoms and MPML laxity. The laxity of the soft-tissue restraint (the MPML), and not a difference in morphological characteristics24, was associated with symptomatic extensor dysfunction. That conclusion is supported by the improvement in the IKDC score following correction of the physical finding of subluxation, which restored the involved knee to the physical state of the contralateral, asymptomatic knee.
The surgical procedures that we performed result in less morbidity than is produced by a tibial tubercle osteotomy done to reduce the Q angle and correct patella alta24. Currently, we rarely do a medial displacement osteotomy of the tibial tubercle, reserving that procedure for patients with a failed MPML plication.
One weakness of this study is the lack of confirmation, by a blinded and unbiased experienced examiner, of the reliability of the physical finding necessary to distinguish the lax MPML from the intact structure. Physical examination of patellar instability has been said to be unreliable, and some experienced examiners therefore rely totally on imaged morphological changes to determine the presence of potential or actual patellar instability24. Although we believe that our findings are valid, the reliability of physical examination in demonstrating this disorder is yet to be determined.
Complications of MPML plication have been minimal. Arthrofibrosis occurred rarely in this series. However, we recently saw a middle-aged patient who developed severe arthrofibrosis postoperatively.
In conclusion, isolated deficiency of the distal-medial soft-tissue patellar restraint, the MPML, may give rise to a clinical syndrome. This syndrome is characterized by distal, medial, and/or lateral knee extensor pain elicited by active terminal knee extension against resistance and lateral patellofemoral tenderness. Other symptoms may include giving-way at terminal knee extension and, in nearly 50% of cases, episodic transient patellar subluxation. The strong association of this syndrome of painful terminal knee extension with a high Q angle and an acute sulcus angle should make the physician suspect isolated MPML deficiency in such cases. The role of the MPML deficiency in this syndrome is supported by the fact that, in patients whose symptoms did not decrease with conservative treatment, the subluxation and associated anterior knee pain and giving-way resolved following successful plication of the MPML.
MPML plication is a low-morbidity, outpatient surgical procedure with which we have had encouraging results. However, the results of this study do not definitively indicate that surgical plication of the MPML is the best treatment for this disorder. It is not known whether nonanatomical isometric MPFL reconstruction performed at the distal attachments at the medial aspect of the femoral epicondyle and the midpart of the patella can effectively prevent these symptoms associated with isolated MPML laxity. A randomized trial with strict selection criteria and long-term follow-up is needed to determine if addressing the MPML deficiency, as was done in this study, is more or less effective than performing a medial displacement osteotomy of the tibial tubercle, with or without MPML plication.
Tables presenting the relative prevalence of different presentations of patellofemoral instability requiring surgical repair, data on individual patients, and preoperative and postoperative IKDC scores are available with the online version of this article on our web site at jbjs.org.
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