The surgical treatment of patellar instability has evolved in response to changing perceptions, an enhanced understanding of the pathologic anatomy, and the introduction of arthroscopy. In 1968, Hughston¹ recognized that patients afflicted with patellar instability were not solely overweight, knock-knee female teenagers as previously believed. He described subluxation of the patella as a significant cause of internal derangement of the knee in athletes. Recently, attention has been focused on the role of injury to the medial patellofemoral ligament (MPFL) as the essential lesion in lateral patellar dislocation. Cadaveric and biomechanical studies have demonstrated its significant contribution as a restraining force against lateral patellar motion.² Surgical exploration of acute dislocations has consistently revealed disruption of the MPFL; operative repair of the ligament was associated with prevention of recurrent dislocation.³ Arthroscopy has been incorporated into the treatment of patellar instability. It provides excellent visualization of associated intra-articular pathology and allows the surgeon to assess patellar tracking. Arthroscopic techniques of lateral release and medial imbrication are also changing the traditional surgical treatment of patellar instability.

Historically, the operative treatment of recurrent patellar dislocation was first addressed in 1888 by Roux⁴ who described the components of patellar realignment, which included a proximal lateral release and medial reefing combined with distal transfer of the patellar tendon insertion. Goldthwait⁵ subsequently modified this technique in 1904 by transferring only the lateral half of the patellar tendon insertion behind the intact medial half with fixation to the pes anserine. Hauser,⁶ in 1938, transferred the entire patellar tendon insertion as a bone block. The tubercle was advanced medially, distally, and also posteriorly due to the downward slope of the medial proximal tibia. This technique has fallen out of favor because posteriorization of the insertion results in increased patellofemoral contact stresses and subsequent degeneration and arthritis.

The Elmslie-Trillat procedure as modified by Cox⁷ combines a medial capsular reefing, a lateral retinacular release, and displacement of the anterior tibial tuberosity medially while hinged on a distal periosteal flap. Designed for correction of patellofemoral malalignment in cases of acute and recurrent patellar subluxations and dislocations, this procedure resulted in minimal recurrence with results directly related to intra-articular pathology and insufficient correction of a wide Q angle or patella alta.

Fulkerson et al.⁸ described anteromedial tibial tubercle transfer for those patients with malalignment and patellar articular degeneration. Anteriorization increases the angle between the patellar tendon and the quadriceps tendon, thus decreasing the patellofemoral joint reaction force. Also, the load is transferred to the more proximal, healthier cartilage from the distal, degenerated cartilage. The procedure is combined with a lateral retinacular release and a medial reefing, if necessary, for more severe subluxation.

The isolated lateral release has also undergone changes in its indications and evolution from open to arthroscopic techniques. Originally described in the American literature by Merchant and Mercer⁹ in 1974, the lateral release of the patella is now recognized as a procedure that is not without complications and should be performed only for specific patellofemoral pathology and not for unexplained anterior knee pain. Kolowich et al.¹⁰ outlined specific indications and contraindications in 1990. Regarding technique, McGinty and McCarthy,¹¹ in 1981, and Metcalf,¹² in 1982, described an arthroscopic controlled lateral release, and subsequently
Fu and Maday,¹³ in 1992, discussed their technique of arthroscopic lateral release in the treatment of patellar tilt and lateral patellar compression syndrome (LPCS).

In this chapter, we present our technique for surgical treatment of patellofemoral instability. The technique incorporates the traditional proximal and distal realignment of the extensor mechanism with an appreciation of the patient population, understanding of the pathologic anatomy with attention to restoration of the balance of the patella, and use of arthroscopy to identify and correct visualized pathology. Also included are indications, contraindications, technical alternatives and pitfalls, postoperative rehabilitation, outcomes, and new directions.

The decision to proceed with realignment of the extensor mechanism for patellar instability is made after careful patient selection, which includes a thorough history and physical examination and appropriate radiographic studies. A description of a detailed physical examination of a patient with suspected patellar instability is beyond the scope of this chapter; however, certain findings suggestive of instability and malalignment deserve mention.^14,15 On inspection, a patient may demonstrate vastus medialis obliquus (VMO) dysplasia, vastus lateralis hyperplasia, patella alta, or lateral patella displacement. On clinical examination, a patient may demonstrate an excessive Q angle or abnormal 90 degree tubercle sulcus angle, lateral pull sign, passive lateral hypermobility of the patella with a positive apprehension sign, and a negative or neutral passive patellar tilt. Findings consistent with isolated lateral patellar compression syndrome would be restriction of medial patellar glide, limitation of passive patellar tilt, peripatellar retinacular tenderness, and a normal Q angle.¹³

For radiographic examination, we obtain a 45-degree posteroanterior flexion weight-bearing view, a lateral view at 30 degrees of flexion, and a Mercer-Merchant view at 45 degrees. Possible findings include a hypoplastic lateral femoral condyle or evidence of trochlear dysplasia with a “crossing sign” as described by Dejour et al.¹⁶ Patellar height can be assessed with the Insall and Salvati¹⁷ index of the ratio of patellar tendon length and the greatest diagonal length of the patella. The Mercer-Merchant view may show lateral patellar subluxation with an abnormal congruence angle of greater than 16 degrees.¹⁸ An additional Laurin view at 20 degrees of flexion may show patellar tilt if the patellofemoral angle does not open laterally.¹⁹ Computed tomography (CT) scans are a useful adjunct if the diagnosis of subluxation is in doubt. The radiographs are further inspected for evidence of osteoarthritis, particularly in the patellofemoral joint, and for loose bodies.

Once the diagnosis of patellar instability or lateral patellar compression syndrome is made, the patient is placed in a supervised rehabilitation program. This program is successful in the majority of patients. A primary indication for operative intervention is continued disability and symptoms of instability in spite of the attempted rehabilitation. For continued instability, we prefer a modified Elmslie-Trillat reconstruction unless there is significant patellofemoral chondrosis, in which case we perform a Fulkerson distal realignment and proximal reconstruction, if necessary. Lateral patellar compression syndrome that does not respond to nonoperative therapy is treated with an isolated arthroscopic lateral release, taking care to preserve the vastus lateralis insertion on the patella.

Another indication for operative management is an acute dislocation with an osteochondral fracture and loose body. Contraindications to these procedures include active infection, unexplained anterior knee pain, and medial patellar instability. The Elmslie-Trillat and Fulkerson procedures are contraindicated in the skeletally immature patient with open proximal tibial growth plates. For these patients, we perform only proximal realignments.