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Medial patellar subluxation (MPS) is a disabling, often iatrogenic patellar instability due to previous lateral release for patellar instability. Lateral release destabilizes the patella on the lateral side, worsening the initial lateral instability and causing MPS. MPS is poorly recognized and may range from subluxation to true dislocation. This report describes a technique developed in response to episodes of medial and lateral patellar subluxation after failed lateral release for patellar instability. The technique uses a graft that extends from the medial patellofemoral ligament origin through the quadriceps tendon to the lateral epicondyle, thereby reconstructing both the medial and lateral patellofemoral ligaments, as well as providing simultaneous stability to both the medial and lateral sides of the patella.
See video under supplementary data.
Patellar instability is a common and disabling condition that can limit daily functional activities because of apprehension and pain. The instability is influenced by a variety of factors that allow the patella to translate laterally and ultimately dislocate. In patients with normal trochlear and patellar osseous anatomy and lower extremity alignment, patellar instability results from deficient soft-tissue stabilizers.
Our technique was developed in response to episodes of medial and lateral patellar subluxation after failed lateral release for patellar instability. The technique uses a tendon graft that extends from the MPFL origin through the quadriceps tendon to the lateral epicondyle, thereby reconstructing both the MPFL and lateral patellofemoral ligament (LPFL) and providing stability to both the medial and lateral sides. An advantage of using the tendon graft through the quadriceps is avoiding bone tunnels, screws, and anchors in the patella, thereby avoiding the risk of patellar fracture. We describe our technique in this report. Table 1 describes the pearls, indications, and pitfalls of this technique.
Table 1Tips, Pearls, Indications, and Pitfalls
Tips and pearls
1. Ensure balanced tracking of the patella in the femoral trochlea first using lateral release and tibial tubercle transfer selectively.
2. The arthroscopic leg holder should be used for all portions of the case.
3. Ensure that a long enough incision is made with adequate skin flaps to palpate the appropriate femoral landmarks.
1. Lateral patellar subluxation with medial subluxation after lateral release
2. Residual instability after patellofemoral joint or total knee arthroplasty
1. Failure to correct underlying malalignment
2. Failure to accurately identify MPFL and LPFL attachment sites
The patient is examined under anesthesia to confirm the diagnosis of medial and lateral patellar instability (Video 1). Medial and lateral forces are applied to the patella in full extension and 30° of flexion. A tourniquet is routinely placed on the thigh, and the patient is then positioned supine with the surgical limb secured in a leg holder. Diagnostic arthroscopy is routinely performed, and intra-articular findings are noted. The patellofemoral joint, in addition to the medial and lateral compartments, is evaluated for the presence of chondral injuries. Chondroplasty is performed as needed, and loose bodies are removed. Associated meniscal pathology is addressed as indicated.
A midline skin incision is made, and skin flaps are developed to expose the patella and patellar mechanism from 5 cm above the patella to the tibial tubercle. Hemostasis is obtained with electrocautery. A lateral release and tibial tubercle transfer may be performed if indicated to center the patella in the trochlea. If autograft is used, the semitendinosus tendon is palpated through the overlying sartorial fascia. The sartorial fascia is incised, exposing the semitendinosus and gracilis tendons adherent to the underlying surface of the fascia. The semitendinosus tendon is released from its insertion and controlled with a clamp. Any secondary soft-tissue attachments are released, and a closed tendon stripper (Smith & Nephew, Andover, MA) is used to release the tendon proximally. The pes fascia is closed with No. 0 Vicryl (Ethicon, Somerville, NJ). The appropriate locations for the femoral attachments of the MPFL and LPFL are identified. A 1-cm incision is made at each site to allow for anchor placement. Two more small incisions are made at both the medial and lateral borders of the quadriceps tendon just at the superior edge of the patella (Fig 1). Subfascial tunnels are then bluntly created with a hemostat between the quadriceps and the MPFL and LPFL attachment sites, respectively (Fig 2). With a No. 11 blade scalpel, a transverse tunnel is made in the distal quadriceps beneath the anterior lamina of the quadriceps tendon (Fig 3). The graft is then passed through both tunnels and the quadriceps, running from medial to lateral through the quadriceps (Fig 4). One end of the graft is prepared with No. 2 FiberLoop (Arthrex, Naples, FL) using the SpeedWhip (Arthrex) technique in the end to be used for the medial femoral attachment. The graft is then secured to the MPFL attachment site with a 4.75 × 24.5–mm Bio-SwiveLock SP suture anchor (Arthrex). After measurement of the correct length for the tendon at the lateral epicondyle, the excess tendon is excised. The cut end of the tendon is secured with No. 2 FiberLoop in a similar fashion. The graft is passed through the lateral subfascial tunnel between the LPFL and quadriceps (Fig 5). The lateral side is then fixed at the LPFL attachment site at the lateral femoral epicondyle with another Bio-SwiveLock SP anchor. Proper graft tension is obtained by holding the knee in 60° of flexion with the patella reduced in the trochlea (Fig 6). Quadriceps contraction is simulated with a towel clip to verify full excursion, and the graft is confirmed to be isometric. Repeat arthroscopy is performed, showing the patella to be centered and stable (Fig 7).
The fascial and skin incisions are closed, and the patient is placed in a knee immobilizer. Postoperatively, the patient is admitted for observation, educated on active range-of-motion and quadriceps exercise, and discharged from the hospital the following day. The patient is encouraged to bear weight as tolerated with crutches for 2 to 4 weeks. The knee immobilizer is discontinued when the patient has gained good quadriceps control.
Several anatomic factors should be considered, although considerable variation exists. The quadriceps tendon includes contributions from the rectus femoris superficially, the vastus medialis and vastus lateralis intermediately, and the vastus intermedius deeply.
Anatomic studies are helpful for determining the optimal position of the graft during reconstruction. The femoral attachment site greatly influences graft isometry, emphasizing the need for accurate tunnel placement on the femur.
Anatomic studies show various origins/insertions of the MPFL, including the medial femoral epicondyle, anterior to the medial femoral epicondyle, superoposterior to the medial femoral epicondyle, and the adductor tubercle.
Several techniques for MPFL reconstruction have been described, and various graft choices have been used with encouraging results. Many of these techniques involve the use of drill holes through the patella, thus risking patellar fracture and violation of the patellar articular surface. Steensen and colleagues
described a technique for MPFL reconstruction using a quadriceps tendon graft that was harvested from the anterior lamina of the quadriceps tendon. The technique avoided a patellar bone block and did not require drill holes through the patella, thereby eliminating the risks of patellar fracture and damage to the articular surface. Their early results were promising, with good or excellent results achieved in 100% of patients and no episodes of patellar dislocation at a mean of 42 months postoperatively.
described a technique for LPFL reconstruction using autogenous tissue as a salvage procedure for repair of medial iatrogenic instability. In their experience, direct repair or imbrication of the lateral retinaculum failed to provide long-term stability because medial excursion usually appeared after 1 year. Their technique used the patient's own quadriceps tendon to re-create the LPFL. They reported excellent results with no cases of recurrent instability, but in 3 of 60 patients, they noted patellar fractures that required open reduction and internal fixation.
MPFL and LPFL reconstruction with a tendon graft through the quadriceps is a simple procedure with little associated morbidity. The technique is effective in preventing further episodes of instability and improving quality of life. A clear advantage of using the tendon graft through the quadriceps is avoiding bone tunnels, screws, and anchors in the patella, thereby avoiding the risk of patellar fracture.
From November 2011 until March 2013, the senior author performed the described technique in 46 knees in 42 patients. The technique was used in cases of MPS after failed lateral release and as part of a stabilization procedure including lateral retinacular lengthening and tibial tubercle transfer for severe patellar instability. The indications also included cases of residual instability after patellofemoral joint replacement or total knee arthroplasty. The early results have been promising. In 44 of 46 cases (95.6%), the patella was stable with no residual medial or lateral subluxation after 1 year of follow-up. There have been no cases of patellar fracture, quadriceps tendon rupture, or infection. Outcome studies are in progress.