Overmedialization Following Tibial Tuberosity Osteotomy
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).
The clinical presentation of a patient with overmedialization of the tibial tuberosity is knee pain resulting from abnormal joint loading progressing to arthrosis.
Most often, the arthrosis is located within the medial patella/trochlea facets and/or the medial compartment of the tibiofemoral joint.
Less commonly, overmedialization of the tibial tuberosity can also be associated with medial patellar instability. As discussed in Chapter 11, medial patellar instability can be problematic. The most frequent complaint is often disabling anterior knee pain.20,21,22,23