Open Repair of the Medial Patellofemoral Ligament and Vastus Medialis Obliquus Muscle

Comprehensive Introduction and Patho-Epidemiology

Patellofemoral instability represents a remarkably complex, multifactorial clinical entity that demands a rigorous, anatomically based approach to both conservative and surgical management. Historically, the treatment of lateral patellar dislocations was fraught with high recurrence rates and unpredictable functional outcomes, largely due to a fundamental misunderstanding of the intricate interplay between osseous geometry and soft-tissue restraints. The medial patellofemoral ligament (MPFL) has since been definitively identified as the primary passive restraint to lateral patellar translation, contributing approximately 50% to 60% of the total restraining force during the critical first 20 to 30 degrees of knee flexion. Beyond this arc of motion, the patella typically engages the trochlear groove, at which point the osseous architecture assumes the predominant stabilizing role. Consequently, any disruption to the MPFL inevitably compromises the delicate kinematic balance of the extensor mechanism, predisposing the joint to recurrent subluxation or frank dislocation.

The vastus medialis obliquus (VMO) serves as the critical dynamic medial restraint, functioning in concert with the static MPFL. The distal muscle fibers of the VMO interdigitate directly with the underlying MPFL, creating a synergistic capsuloligamentous complex that actively centers the patella within the trochlea during early flexion. In the event of an acute lateral patellar dislocation, biomechanical and magnetic resonance imaging (MRI) studies have demonstrated that the MPFL is virtually always torn. The most common pattern of failure involves an avulsion from its femoral origin near the adductor tubercle, accounting for up to 60% of cases, although midsubstance ruptures and patellar-sided avulsions are also frequently observed. The precise location of this failure dictates the surgical approach, as primary repair is highly dependent on the availability of robust, bleeding osseous beds and viable ligamentous tissue.

Epidemiologically, acute patellar dislocations occur most frequently in the second and third decades of life, with a pronounced predilection for active, athletic populations. The incidence is estimated at 5.8 to 7.0 per 100,000 in the general population, but this figure approaches 30 per 100,000 in the adolescent demographic. The classic mechanism of injury involves a non-contact pivoting motion, characterized by internal rotation of the femur on a fixed, externally rotated tibia with the knee in slight flexion and valgus alignment. This generates a massive lateral vector force that overwhelms the medial restraints. While conservative management remains the first-line treatment for the majority of primary dislocations, the recurrence rate following non-operative treatment can approach 40% to 50%, particularly in patients with underlying pathoanatomic risk factors such as trochlear dysplasia, patella alta, or an elevated tibial tubercle-trochlear groove (TT-TG) distance.

Open repair of the MPFL combined with VMO imbrication or advancement is a highly specific, targeted procedure. In contemporary orthopedic practice, the paradigm has shifted heavily toward anatomical MPFL reconstruction utilizing autograft or allograft tissue, particularly for chronic instability or recurrent dislocations. However, direct open repair remains a highly viable, tissue-sparing option for a carefully selected subset of acute cases. Specifically, when an acute femoral avulsion can be anatomically reduced to bone in a patient without profound osseous dysplasia, primary repair can restore native kinematics without the morbidity associated with graft harvest or the technical complexities of tunnel placement. This chapter exhaustively details the anatomical foundations, precise indications, meticulous surgical techniques, and postoperative protocols required to execute this procedure successfully.

Detailed Surgical Anatomy and Biomechanics

A profound mastery of the medial knee anatomy is non-negotiable for any surgeon undertaking patellofemoral stabilization. The medial structures of the knee are classically divided into three distinct layers, as described by Warren and Marshall. Layer 1 comprises the deep crural fascia, which invests the sartorius muscle and blends anteriorly with the medial retinaculum. Layer 2 contains the superficial medial collateral ligament (sMCL) and the MPFL. The MPFL is situated deep to the VMO and superficial to the joint capsule, extending from the medial border of the patella to the medial aspect of the distal femur. Layer 3 consists of the true joint capsule and the deep medial collateral ligament. The critical surgical plane for MPFL isolation lies between Layer 1 and Layer 2, requiring meticulous dissection to avoid inadvertent capsular penetration or damage to the delicate ligamentous fibers.

The femoral origin of the MPFL is a highly specific anatomical footprint that must be precisely identified to ensure isometric or near-isometric repair. This origin is located in a saddle-shaped depression situated between the adductor tubercle superiorly and the medial epicondyle inferiorly. Radiographically, this point was elegantly defined by Schöttle et al. on a true lateral radiograph: 1 mm anterior to the posterior cortical line of the femoral diaphysis, 2.5 mm distal to the posterior origin of the medial femoral condyle, and proximal to the level of the posterior point of Blumensaat's line. The patellar insertion is broader, attaching to the proximal half to two-thirds of the medial patellar margin, often blending intimately with the undersurface of the VMO and the quadriceps tendon. The native MPFL has a mean length of 50 to 60 mm and a highly variable width, typically resembling a thin, sail-like fascial band rather than a robust, cord-like ligament.

Biomechanically, the MPFL is a check-rein rather than a continuous tension band. It exhibits a tensile strength of approximately 208 Newtons, which is relatively low compared to the cruciate ligaments, explaining its near-universal failure during a lateral dislocation event. The MPFL is most taut in full extension and early flexion (0 to 30 degrees), precisely the arc of motion where the patella lacks the bony containment of the trochlear groove. As the knee flexes beyond 30 degrees, the patella engages the trochlea, and the MPFL normally becomes lax. This kinematic reality dictates the fundamental rule of medial-sided surgery: the repair or reconstruction must be tensioned at 30 degrees of flexion to prevent over-constraint. Tensioning the ligament in full extension will result in catastrophic overtightening as the knee flexes, leading to medial facet overload, severe pain, and rapid chondral degradation.

The vastus medialis obliquus (VMO) provides the dynamic counterpart to the static MPFL. The VMO fibers originate from the adductor magnus tendon and the medial intermuscular septum, inserting onto the superomedial border of the patella at an angle of 50 to 55 degrees relative to the femoral shaft. This oblique orientation is exquisitely designed to generate a medially directed vector force that counteracts the inherent lateral pull of the vastus lateralis and the iliotibial band. In the setting of an acute dislocation, the VMO is frequently stretched, torn, or functionally inhibited due to joint effusion and pain (arthrogenic muscle inhibition). Open surgical repair therefore necessitates not only the reattachment of the MPFL but also the advancement and imbrication of the VMO to restore this critical dynamic medial vector, effectively re-establishing the synergistic capsuloligamentous complex that dictates normal patellar tracking.

Exhaustive Indications and Contraindications

The decision to perform an open repair of the MPFL and VMO, as opposed to conservative management or formal MPFL reconstruction, rests on a highly nuanced evaluation of the patient's pathoanatomy, chronicity of injury, and functional demands. The historical "Low Risk—Low Reward" paradigm associated with isolated medial repairs stems from unselected cohorts where repairs were performed in the presence of severe underlying osseous dysplasia, leading to unacceptable failure rates approaching 30%. Therefore, modern indications for this procedure are exceedingly strict. The ideal candidate is a patient with a first-time, acute lateral patellar dislocation who possesses a distinct, MRI-confirmed avulsion of the MPFL from its femoral origin, accompanied by normal or near-normal underlying osseous geometry (TT-TG < 20 mm, normal Insall-Salvati ratio, and minimal trochlear dysplasia).

Another absolute indication for acute surgical intervention is the presence of an osteochondral fracture that requires internal fixation or removal. During a lateral dislocation, the medial facet of the patella frequently impacts the lateral femoral condyle as it dislocates or during spontaneous reduction. This shear force can create substantial osteochondral loose bodies. When arthroscopy is indicated to address these lesions, concurrent open repair of an acutely avulsed MPFL is highly recommended, as the joint is already being accessed and the biological healing potential of the acute avulsion is optimal. Furthermore, high-level athletes who suffer an acute dislocation near the end of their season may be candidates for acute repair to expedite their return to sport, provided their tissue quality is robust and the tear pattern is amenable to primary anchor fixation.

Conversely, the contraindications for open primary repair are numerous and must be strictly respected to avoid surgical failure. Chronic patellofemoral instability is an absolute contraindication for primary repair. In the chronic setting, the MPFL tissue is attenuated, scarred, and mechanically incompetent; attempting to repair or imbricate this poor-quality tissue will inevitably lead to recurrent stretching and failure. For chronic dislocators, anatomical MPFL reconstruction using an autograft (e.g., gracilis or semitendinosus) or allograft is the undisputed gold standard. Similarly, midsubstance tears of the MPFL are generally poor candidates for primary repair, as the thin, fascial nature of the midsubstance tissue does not hold sutures well, and end-to-end repairs in this zone have demonstrated inferior biomechanical outcomes compared to reconstruction.

Severe osseous malalignment represents another critical contraindication to isolated soft-tissue repair. If a patient presents with a TT-TG distance greater than 20 mm, profound patella alta (Caton-Deschamps index > 1.2), or high-grade trochlear dysplasia (Dejour Type C or D), isolated MPFL repair will fail because the soft tissues cannot overcome the massive lateral vector forces generated by the underlying bony architecture. In these scenarios, the osseous abnormalities must be addressed concurrently through distal realignment procedures (e.g., Fulkerson or Elmslie-Trillat osteotomies) or, in highly selected cases, trochleoplasty. Finally, patients with generalized ligamentous laxity or connective tissue disorders (e.g., Ehlers-Danlos or Marfan syndrome) are strictly contraindicated for primary repair, as their inherent collagen defects will result in rapid attenuation of the repaired construct.

Pre-Operative Planning, Templating, and Patient Positioning

Thorough preoperative planning is the cornerstone of successful patellofemoral surgery. The evaluation begins with a meticulous clinical examination, ideally performed bilaterally to establish the patient's baseline ligamentous laxity. The apprehension test is the hallmark of patellofemoral instability; it is elicited by applying a laterally directed force to the patella with the knee flexed to 20 to 30 degrees. A positive test is characterized by patient guarding, quadriceps contraction, and a subjective feeling of impending dislocation. The lateral glide test quantifies the degree of MPFL incompetence. The patella is divided into four longitudinal quadrants; lateral translation of greater than 2.5 to 3 quadrants, or the lack of a firm endpoint, signifies gross disruption of the medial restraints. Additionally, the surgeon must assess for the "J-sign," which indicates abnormal tracking and delayed trochlear engagement, often associated with patella alta and lateral tightness.

Radiographic assessment is mandatory and must include a comprehensive series: weight-bearing anteroposterior (AP), true lateral, and axial (Merchant or Sunrise) views. The true lateral radiograph is critical for evaluating patellar height and trochlear morphology. Patella alta is quantified using the Insall-Salvati ratio (patellar tendon length divided by patellar bone length; normal is 1.0, >1.2 indicates alta) or the Caton-Deschamps index. Trochlear dysplasia is identified on the lateral view by the presence of the "crossing sign" (where the trochlear groove line crosses the anterior border of the lateral condyle), a supratrochlear bump, or double contour. Axial views allow for the measurement of the sulcus angle; an angle exceeding 140 degrees is indicative of a shallow, dysplastic trochlea.

Advanced imaging with MRI and computed tomography (CT) is indispensable. MRI is the modality of choice for characterizing the acute soft-tissue injury. It precisely localizes the MPFL tear—whether it is a femoral avulsion, midsubstance rupture, or patellar avulsion—and identifies the classic bone bruising pattern associated with lateral dislocations (contusion of the medial patellar facet and the lateral femoral condyle). MRI is also highly sensitive for detecting osteochondral lesions that may require concurrent fixation. CT scanning is utilized primarily to measure the TT-TG distance, which dictates the need for a distal realignment osteotomy. The TT-TG is measured by superimposing axial cuts of the deepest part of the trochlear groove and the apex of the tibial tubercle. A distance of less than 15 mm is normal, 15 to 20 mm is borderline, and greater than 20 mm is distinctly abnormal and typically necessitates an anteromedialization or straight medialization procedure.

In the operating room, meticulous patient positioning is essential to facilitate both dynamic assessment and the surgical approach. The patient is placed supine on the operating table. A lateral thigh post or a standard leg holder is utilized, ensuring that the knee can be freely flexed from 0 to at least 120 degrees without obstruction. A proximal thigh tourniquet is applied; however, it is heavily advised to leave the tourniquet uninflated unless visualization becomes critically compromised by hemorrhage. Performing the procedure without a tourniquet allows the surgeon to accurately assess the resting tension of the VMO and the extensor mechanism, preventing iatrogenic over-constraint during the imbrication phase. Prior to prepping and draping, an Examination Under Anesthesia (EUA) is performed to dynamically confirm the degree of lateral translation and to evaluate the tracking of the patella throughout the full arc of motion.

Step-by-Step Surgical Approach and Fixation Technique

Diagnostic Arthroscopy and Joint Preparation

The procedure invariably commences with a comprehensive diagnostic arthroscopy. Standard anterolateral and anteromedial portals are established. In the acute setting, a significant hemarthrosis is typically present and must be thoroughly evacuated to permit adequate visualization. The joint is meticulously inspected for osteochondral loose bodies, which frequently shear off the medial patellar facet or the lateral femoral condyle during the dislocation or reduction event. Any salvageable osteochondral fragments are prepared for internal fixation, while non-viable fragments are excised, and the donor beds are debrided or microfractured. Crucially, the surgeon must dynamically assess patellofemoral tracking through a superolateral viewing portal. By observing the patella as it enters the trochlea from 0 to 30 degrees of flexion, the surgeon can visually confirm the lack of medial restraint and establish a baseline for comparison following the open repair.

Surgical Approach and Superficial Dissection

Following the arthroscopic phase, attention is turned to the open medial approach. A 4-cm to 5-cm oblique incision is centered over the adductor tubercle and the medial epicondyle. The incision is ideally oriented in line with the skin cleavage planes (Langer’s lines) to optimize cosmetic healing, which is particularly important in the younger demographic typical of this injury. The dissection is carried down through the subcutaneous tissue to the deep crural fascia. At this juncture, meticulous identification and protection of the infrapatellar branch of the saphenous nerve are paramount. This nerve courses anteriorly and inferiorly across the medial aspect of the knee; iatrogenic transection or entrapment in scar tissue will result in painful neuromas and debilitating medial numbness. The covering fascia is incised in line with the skin incision, granting access to Layer 2 of the medial knee.

Identification of the MPFL and VMO

The distal muscular belly of the vastus medialis obliquus is identified. Using a blunt retractor, such as a small Richardson or Army-Navy, the VMO is gently mobilized and retracted superiorly and anteriorly. This maneuver exposes the underlying joint capsule and the critical femoral origin of the MPFL. The surgeon must carefully inspect the MPFL tissue and the adductor tubercle. In an acute avulsion, a distinct hematoma and a bare bony footprint in the saddle region between the adductor tubercle and the medial epicondyle will be evident. The avulsed edge of the MPFL is identified, tagged with a traction suture, and its tissue quality is assessed to ensure it possesses sufficient tensile integrity to hold the repair sutures.

Ligament Repair and Fixation Technique

The specific fixation technique is dictated by the precise nature of the tissue failure. If a robust residual stump of soft tissue remains attached to the adductor tubercle, a direct end-to-end soft-tissue repair is performed using heavy, nonabsorbable braided sutures (e.g., #2 FiberWire or Ethibond) in a Krackow or locking Mason-Allen configuration. However, the more common scenario involves a direct avulsion from the bone. In this case, the anatomical footprint at the adductor tubercle is prepared with a curette or rasp to decorticate the bone, creating a bleeding bed that promotes robust biological healing. One or two double-loaded suture anchors (typically 4.5 mm to 5.5 mm in diameter, utilizing PEEK, biocomposite, or all-suture technology) are inserted into the prepared footprint. The sutures are passed through the avulsed edge of the MPFL using a free needle or a suture passing device.

Tensioning and VMO Imbrication

The most critical step of the procedure is the tensioning of the repair. The knee MUST be placed in 30 degrees of flexion prior to tying the sutures. At this angle, the patella is naturally engaged within the trochlear groove. The sutures are tied with just enough tension to eliminate gross laxity; the MPFL is a check-rein, not a tension band. The surgeon must verify that the patella is centered but can still be passively glided laterally by 1 to 2 quadrants. Overtightening is the most common and devastating error in this procedure. Once the MPFL is secured, the VMO is advanced distally and laterally over the repair site to provide dynamic reinforcement. The VMO fascia is sutured to the medial border of the patella and the medial retinaculum using interrupted absorbable sutures (e.g., #1 Vicryl), ensuring appropriate resting tension without restricting knee flexion. A final arthroscopic check can be performed to confirm centralized tracking without medial compartment overload.

Complications, Incidence Rates, and Salvage Management

Despite meticulous surgical technique, open repair of the MPFL and VMO carries a specific risk profile that the orthopedic surgeon must be prepared to manage. The most frequent and arguably the most devastating technical complication is iatrogenic over-tensioning of the medial structures. When the MPFL is repaired with the knee in full extension, or if the femoral anchors are placed too proximally or anteriorly relative to Schöttle's point, the ligament will become excessively tight as the knee flexes. This non-isometric fixation dramatically increases the joint reaction forces across the medial patellofemoral compartment. Clinically, this presents as severe, intractable postoperative anterior knee pain, a profound loss of terminal flexion, and rapid, progressive chondral degradation of the medial facet. Management of severe over-tensioning often requires early surgical release or revision reconstruction to prevent irreversible arthrosis.

Recurrent instability is another significant complication, historically reported in up to 20% to 30% of unselected primary repair cohorts, though this rate is dramatically lower when strict indications (acute avulsions, normal osseous geometry) are applied. Failure is almost universally due to the surgeon's failure to recognize and address concurrent osseous malalignment, such as a TT-TG distance exceeding 20 mm or severe trochlear dysplasia. When the soft-tissue repair is subjected to overwhelming lateral vector forces, the sutures will pull through the tissue, or the ligament will plastically deform and attenuate. Salvage management for recurrent instability following a failed primary repair mandates a comprehensive reassessment of the bony architecture. The definitive salvage procedure typically involves an anatomical MPFL reconstruction utilizing autograft or allograft, combined with a distal realignment osteotomy (e.g., Fulkerson or Elmslie-Trillat) to normalize the vector mechanics.

Postoperative stiffness and arthrofibrosis are risks inherent to any open knee surgery, particularly when the joint capsule and extensor mechanism are manipulated. The incidence of clinically significant stiffness requiring intervention is approximately 5% to 8%. This is heavily mitigated by adherence to an accelerated rehabilitation protocol that emphasizes immediate passive and active-assisted range of motion. If a patient fails to achieve 90 degrees of flexion by 6 weeks postoperatively despite aggressive physical therapy, manipulation under anesthesia (MUA) and arthroscopic lysis of adhesions should be strongly considered.

Nerve injury is a highly specific complication related to the surgical approach. The infrapatellar branch of the saphenous nerve is highly vulnerable during the medial incision and superficial dissection. Injury to this nerve occurs in approximately 10% to 15% of cases and can result in localized neuromas, hyperesthesia, or a dense patch of numbness over the anteromedial aspect of the proximal tibia. While numbness is generally well-tolerated, a painful neuroma may require surgical excision and burying of the nerve stump into the adjacent muscle belly. Superficial and deep surgical site infections are rare (<2%) but require prompt recognition, aggressive irrigation and debridement, and culture-directed antibiotic therapy to protect the joint and the integrity of the repair.

Phased Post-Operative Rehabilitation Protocols

The postoperative rehabilitation protocol following open MPFL and VMO repair must strike a delicate balance: it must protect the healing medial capsuloligamentous structures from excessive lateral shear forces while simultaneously preventing arthrofibrosis and profound quadriceps atrophy. An accelerated, phased rehabilitation program is currently the standard of care, requiring close communication between the operating surgeon and the physical therapy team.

Phase I: Maximum Protection (Weeks 0–2)

The primary goals of the initial phase are to control postoperative pain and effusion, initiate early range of motion, and activate the quadriceps musculature. Weight-bearing as tolerated (WBAT) is permitted immediately, provided the knee is locked in full extension in a hinged knee brace. Locking the brace in extension prevents the quadriceps from firing during the stance phase of gait, thereby minimizing stress on the VMO advancement. Immediate postoperative motion is critical to nourish the articular cartilage and prevent capsular adhesions. Passive and active-assisted range of motion from 0 to 90 degrees is encouraged. Muscle activation begins on postoperative day one with isometric quadriceps sets, ankle pumps, and straight-leg raises (performed strictly within the locked brace) to prevent VMO atrophy and inhibit arthrogenic muscle shutdown.

Phase II: Moderate Protection (Weeks 2–6)

As the soft tissues begin to lay down early collagenous matrix, the focus shifts to restoring full range of motion and initiating protected strengthening. The hinged brace is gradually unlocked to allow progressive flexion as tolerated, with a goal of achieving 120 degrees of flexion by week 6. Early strengthening emphasizes closed-kinetic-chain exercises, such as mini-squats, wall slides, and leg presses, strictly limited to a safe arc of 0 to 45 degrees. Closed-chain exercises are highly favored because they increase joint compressive forces, which actively stabilizes and centers the patella within the trochlear groove, thereby protecting the healing MPFL from excessive lateral shear stress. Open-chain knee extensions are strictly contraindicated during this phase, as they place maximum isolated stress on the medial repair and generate high patellofemoral contact pressures.

Phase III: Early Return to Function (Weeks 6–12)

By the sixth postoperative week, the biological healing of the soft tissues is sufficiently advanced to permit the discontinuation of the hinged knee brace, contingent upon the patient demonstrating excellent quadriceps control without an extensor lag during a straight-leg raise. The rehabilitation focus transitions to functional strengthening, proprioception, and normalizing gait mechanics. Range of motion should be full and symmetric to the contralateral limb. Strengthening exercises are progressed in intensity, incorporating step-ups, step-downs, and stationary cycling with increasing resistance. Proprioceptive training using balance boards and unstable surfaces is introduced to retrain the neuromuscular control of the lower extremity, which is frequently compromised following a dislocation event.

Phase IV: Advanced Activity and Return to Sport (Weeks 12+)

The final phase of rehabilitation bridges the gap between functional recovery and the demands of competitive athletics. Advanced agility drills, plyometrics, and sport-specific exercises are gradually introduced. Straight-line jogging can typically commence around 12 to 14 weeks, progressing to cutting and pivoting maneuvers as strength and confidence improve. The criteria for unrestricted return to competitive sports are rigorous and objective. Return to play is typically permitted between 4 and 6 months postoperatively, contingent upon the patient achieving a minimum of 90% limb symmetry index (LSI) in quadriceps and hamstring strength on isokinetic testing, excellent performance on functional hop tests, and a complete absence of apprehension or effusion during high-demand activities.

Summary of Landmark Literature and Clinical Guidelines

The evolution of surgical decision-making in patellofemoral instability is deeply rooted in several landmark biomechanical and clinical studies. Historically, the seminal work by Conlan, Farkas, and Craig in the early 1990s definitively established the MPFL as the primary medial restraint, fundamentally shifting the focus of instability surgery away from indiscriminate lateral releases and non-anatomic medial reefing toward targeted MPFL restoration. Subsequent biomechanical cadaveric studies by Amis and colleagues precisely quantified the tensile strength and kinematic behavior of the MPFL, establishing the critical principle that the ligament functions as a check-rein in early flexion and must not be tensioned in full extension.

The clinical outcomes of primary MPFL repair have been the subject of intense debate. Early literature, notably studies by Sallay and Nomura, demonstrated the high prevalence of MPFL avulsions in acute dislocations and reported satisfactory outcomes following primary repair in carefully selected patients. However, as the procedure gained popularity, it was frequently applied to unselected cohorts with significant underlying osseous malalignment. This led to high-profile papers reporting failure rates approaching 30%, which catalyzed the modern shift toward MPFL reconstruction. The work of Camp, Erickson, and the International Patellofemoral Study Group has since clarified the "Low Risk—Low Reward" paradigm: isolated repair is statistically comparable to conservative treatment in generalized cohorts, but it remains a highly effective, tissue-sparing option specifically for acute, MRI-confirmed femoral avulsions in patients with normal underlying anatomy.

The integration of osseous geometry into the treatment algorithm was revolutionized by the Lyon School of Knee Surgery, spearheaded by Henri Dejour and later David Dejour. Their classification of trochlear dysplasia and the standardization of the TT-TG measurement on CT scans provided surgeons with the objective metrics required to identify when soft-tissue repair alone would inevitably fail. The current clinical guidelines, heavily influenced by these landmark contributions, dictate a strict, algorithmic approach: primary repair is reserved for acute, anatomically reducible avulsions without bony dysplasia; reconstruction is the gold standard for chronic or midsubstance failures; and distal realignment osteotomies are mandatory when the TT-TG exceeds