Tibial tuberosity osteotomy is a commonly employed surgical technique for the treatment of patellar instability and/or anterior knee pain associated with patellar chondrosis.¹,²,³,⁴

Typically, the tuberosity is transferred medially or anteromedially as an effort to decrease the quadriceps angle (Q-angle) or to unload a compromised lateral patellar facet.⁵ The literature is replete with supportive studies demonstrating efficacy.¹,⁶,⁷

However, the iatrogenic creation of overmedialization can result if a preoperative assessment of tibial tuberosity location has not been considered.

When performing a medialization of the tibial tuberosity, the intent is to normalize the extensor mechanism alignment.

The implication is that the preoperative alignment is abnormal as assessed by the Q-angle and/or the tibial tuberosity-trochlear groove (TT-TG) distance, or the tibial tuberosity-posterior cruciate ligament (TT-PCL) distance. These measurements should be used as guidelines and not absolutes.

There is a variation in agreements for the measurements of TT-TG distance depending upon the imaging technique used (magnetic resonance imaging [MRI] vs computed tomography [CT]) and for the clinical estimates of the Q-angle.⁶,⁸,⁹,¹⁰,¹¹

There are measurement errors for TT-TG distance as well. When TT-TG measurements were performed on two consecutive CT scan for the same knee, there was a mean difference of 3.2 mm (range 0-13 mm). Thus, preoperative measurements of TT-TG distance should be used as guidelines (not absolute values) and should be integrated with clinical estimation of tibial tubercle lateralization.¹²

With the knee in extension, the normal TT-TG distance has been described as 12 mm with a cutoff of “normal” at 20 mm.¹⁰,¹³

During patellar stabilization surgery, it is recommended to medialize tibial tubercle if TT-TG distance is greater than 20 mm. However, a recent study reported on favorable clinical outcomes after isolated medial patellofemoral ligament (MPFL) reconstruction in 19 patients with TT-TG greater than 20 mm. Thus, TT-TG distance greater than 20 mm may not be an absolute indication for medialization of tibial tubercle.¹⁴

In another study, tibial tubercle medialization greater than 10 mm was associated with worse clinical outcomes, irrespective of preoperative or postoperative TT-TG distance.¹⁵

Besides TT-TG distance, clinical evaluation of quadriceps vector (Q-angle in extension and trochlear-sulcus angle in 90° flexion) should be taken into consideration prior to tibial tubercle medialization to avoid overcorrection.¹⁶

If the TT-TG distance is reduced to 8 mm or less, there is a risk for overmedialization.

It has been said that “The knee is a coupled mechanical system. One cannot change any one part of the system without affecting the remaining parts of the system” (personal communication: Tony Valdevit).

When considering tibial tuberosity osteotomy and the potential for overmedialization, the potential adverse effects upon joint loading should be considered.¹⁷,¹⁸,¹⁹