CHAPTER 12 Tibial Tubercle Transfer

The goal of patellofemoral stabilization surgery is central, tracking of the patella in the femoral trochlea. If stable tracking can be achieved using nonoperative means such as core stability physical therapy, and bracing, surgery should be avoided. The caregiver should also rule out retinacular^1,2 or articular^3,4 pain causing the knee to give way. A thorough history and examination,⁵ using pain diagrams⁶ as needed, is central to accurate diagnosis and appropriate surgical planning. Unfortunately, many patients with recurrent patellar instability require some form of stabilization to function adequately in work and daily life, particularly in more vigorous activities. This is particularly important because chronic lateral patellofemoral articular overload may eventually cause joint breakdown.⁷ Debate continues regarding the evolution of trochlea dysplasia,^8,9 but it is likely that chronic lateral facet overload from lateral patellar tracking¹⁰ may contribute to or cause deficiency of lateral trochlear containment of the patella.

It must be considered that balanced patellar tracking with optimal load distribution across the joint is best for patients and presumably minimizes risk of eventual cartilage deterioration and arthritis. Therefore, balanced tracking is of paramount importance. Multiple factors are involved in patellar tracking, including femoral version, tibial version, articular geometry, lower extremity kinematic function, muscle imbalance, foot and ankle mechanics, ligamentory balance of the knee, varies, valgus, body habitus, and posture. Some of these are correctable by nonoperative measures and should therefore be addressed before considering surgery.¹¹ Certainly, an articular lesion causing symptoms of giving way may be mistaken for patellar instability and should be treated appropriately, whether by simple débridement¹² or articular resurfacing.^13–18

Procedures such as trochleoplasty and femoral and tibial derotation may be appropriate in rare patients but carry risks that many surgeons and patients find unacceptable. Therefore, traditional patellofemoral stabilization, using lateral release, medial retinacular restoration (medial patellofemoral ligament [MPFL] imbrication or reconstruction), and/or medial tibial tubercle transfer remain mainstays of patellofemoral stabilization. Lateral release^19–22 has been used widely in the past but has little relevance as an isolated procedure for patients with patellar instability²³ and can cause medial patellar instability²⁴ when used extensively or inappropriately.

The art of patellofemoral stabilization is to determine how best to achieve balanced patellar tracking with minimal long- and short-term risk. This is different for each patient and becomes more challenging as the degree of instability increases.

Restoration of patellofemoral balance by MPFL–medial capsule imbrication, often with release of a lateral retinaculum that has become adaptively tight, is desirable, particularly because it is known that the injured MPFL does heal,²⁵ albeit elongated, in most patients. Sometimes, a tendon graft needs to be added to ensure adequate medial retinacular–MPFL support of the patella,²⁶ but this should be done selectively, when less invasive surgery is judged to be insufficient. Many patients with less serious instability are happy to undergo a smaller procedure with the knowledge that another procedure might be needed in the future. This is occasionally preferable to the alternative risk of surgical complication from a more major surgical intervention. In any case, however, it is important to consider that the MPFL is an important restraint to lateral patellar instability^27–29; be prepared to restore or reconstruct it selectively once adequate patellar tracking alignment had been ensured. Most important in this type of surgery is to avoid excessive patellofemoral joint loading, because the MPFL is a posteriorly oriented structure (Fig. 12-1). Tibial tubercle transfer is the best way to restore proper tracking of the patella in the trochlea in many cases, after which retinacular balance, including the MPFL, can be restored by imbrication or tendon graft reconstruction but without exerting force on the patella. Following tibial tubercle transfer balancing of the extensor mechanism, however, MPFL restoration is often unnecessary, because it usually adapts over time.

FIGURE 12-1 Pulling the patella from lateral to medial with an MPFL graft risks overloading the patellofemoral joint. Balance tracking first.

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