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Distal realignment for patellofemoral disease


OVERVIEW

Chapter synopsis

  • Tibial tuberosity osteotomy (TTO), often performed in conjunction with other proximal realignment procedures, is an effective treatment to address patellofemoral instability, patellar and trochlear focal chondral defects, and patellofemoral arthritis. TTO is a powerful tool that can normalize patellar tracking, alter patellofemoral forces, and optimize loads across the patellofemoral joint in patients with patellofemoral disease. Patellofemoral pathology is often multifactorial in nature. Proper management requires approaching the knee joint as an organ through a comprehensive and systematic evaluation of each patient.

Important points

  • Tibial tuberosity surgery is most commonly performed as a component of a comprehensive approach to patellofemoral compartment pathology.

  • TTO can unload the patellofemoral joint and/or correct multiplanar alignment abnormalities of the patellofemoral joint and extensor mechanism of the knee.

  • Anteromedialization (AMZ) of the tibial tubercle is indicated as a means of tibial tuberosity anteriorization and medialization in patients with patellofemoral chondrosis or in combination with cartilage restoration procedures to normalize alignment and unload the affected compartment while correcting a lateralized force vector.

  • Tibial tuberosity distalization is indicated for patients with patellar instability in the setting of significant patella alta (elevated Caton-Deschamps ratio >1.4).

  • Tibial tuberosity medialization (TTM) is indicated for an increased tibial tuberosity–trochlear groove (TT-TG) and or tibial tuberosity-posterior cruciate ligament (TT-PCL) distance to correct a lateralized force vector in the setting of patellar instability without patellofemoral chondrosis.

  • Medializing TTO is contraindicated in patients with a normal TT-TG distance where the major deformity is not a lateralized tubercle or a medialized groove (i.e., axial malrotation), and with areas of chondrosis that would be subjected to increased loads after medializing TTO (see exception below).

  • TTO is contraindicated in patients with standard contraindications to osteotomy, such as smokers, elevated body mass index (BMI), non-compliant patients, etc.

  • In patients with normal position of the tibial tuberosity, straight tibial tuberosity anteriorization may decrease patellofemoral loading in certain applications.

  • TTO is contraindicated in isolation for central, medial and panpatellar chondrosis, unless concomitant cartilage restoration procedures are being performed to address the cartilage defect. The combination of cartilage restoration with TTO (when specific chondral lesions are noted) may allow improved outcomes compared with either procedure alone.

  • TTO is contraindicated when the site of axial abnormality is external to the tuberosity. For example, excessive hip anteversion or tibial torsion distal to the tuberosity.

  • Patients with symptomatic patellofemoral chondrosis may have painful effusions, patellofemoral crepitation, and loose bodies associated with mechanical symptoms. Patients may have a history of patellar instability or dislocation.

  • TTO is utilized either alone or in conjunction with other patellofemoral procedures when previous non-surgical and other surgical interventions have failed.

Clinical and surgical pearls

  • The goal for all tuberosity surgeries is “normalization” of the tuberosity position and patellar position (in the case of distalization), not overcorrection.

  • Although computerized tomography (CT) scans are not obtained routinely, most patients have undergone a magnetic resonance imaging (MRI) evaluation, which is useful for defining the location and extent of chondrosis. This will aid in selecting the appropriate type of TTO (e.g., AMZ to unload a distal lateral area of chondrosis).

  • Lateralized force vector can be measured on MRI using the TT-TG or TT-PCL distance. When evaluated the lateralized force vector, the TT-TG angle may be a more precise measurement compared to the change in tuberosity distance. Patella height is measured using the Caton-Deschamps ratio more commonly than the Patella Trochlear Index.

  • The mean TT-TG distance of asymptomatic patients is 10–13 mm.

  • The TT-TG distance that serves as a soft threshold for abnormal is above 20 mm and >24 mm for TT-PCL. An individualized approach to each patient should be taken, so that the measured distances are not absolute indications for surgery, but should direct the surgeon to consider TTO.

  • The degree of AMZ should be adjusted to fit each specific patient, with 60° as the steepest AMZ angle. Thus, 10 mm and 15 mm of anteriorization would result in medialization of approximately 6 mm and 9 mm respectively, thus normalizing the elevated TT-TG distances in the majority of patients.

  • An elevated Caton-Deschamps ratio >1.4 (patella alta) would lead the surgeon to consider that a component of distalization be added to normalize the position of the patella.

  • Always measure hip internal and external rotation in the prone position. The presence of excessive clinical hip internal rotation points to possible elevated femoral anteversion, which should then be evaluated with a lower extremity CT version study (hip, knee, and ankle). This CT would also detect excessive tibial external rotation.

  • Preoperative rehabilitation prepares the patient for surgery and optimizes their recovery.

  • Core-to-floor rehabilitation must emphasize proximal and core musculature in addition to local muscles throughout the lower extremity and extensor mechanism

  • Pain that is disproportionate to what is expected postoperatively for a specific surgery in the immediate short term can be concerning for compartment syndrome, but in the intermediate term points towards the potential development of a complex regional pain syndrome (CRPS). Early intervention (including sympathetic blocks) may avoid progression to classic CRPS.

Clinical and surgical pitfalls

  • Overmedialization and/or overdistalization increases patellofemoral forces and may lead to patellofemoral chondrosis and arthrosis. The goal should be the normalization of the TT-TG distance and Caton-Deschamps ratio, while avoiding overcorrection.

  • Medial tibiofemoral forces also increase with tuberosity medialization; be careful in considering a medializing TTO in a varus knee to avoid acceleration of medial compartment wear. Thus, it is important to obtain full-length mechanical axis alignment views of the bilateral lower extremities preoperatively.

  • Educate patients preoperatively of the expected pain related to hardware and the potential need for removal.

  • AMZ osteotomy involves two of three tibial cortices and significantly weakens the tibia until healed. Early full weight-bearing will lead to an increased tibial fracture rate.

  • TTO cannot substitute for correction of pathological laxity of the proximal medial patellofemoral restraints and associated patellar instability. In these cases, the surgeon should first correct bony malalignment and then add a soft tissue procedure to address pathologic laxity (e.g., MPFL reconstruction).

  • Lateral lengthening in conjunction with tibial tuberosity surgery is often used to balance the soft tissue in cases of lateral tightness and fixed patella tilt. Overzealous lateral release may lead to medial iatrogenic dislocations and a paradoxical increase in lateral instability.

  • TTO is contraindicated when the lateral positioning of the patella is secondary to a combination of excessive femoral anteversion and tibial external rotation.

  • In patients with extreme trochlear dysplasia, those with a proximal “bump” at the entrance to the trochlea may benefit from a “Peterson bumpectomy” to avoid the bump continuing to interfere with patellar tracking.

  • Overanteriorization can cause problems with skin healing and may significantly rotate the patella, resulting in abnormal contact stresses.

  • AMZ outcomes are poor in the presence of proximal pole and panpatellar chondrosis or trochlear chondrosis when osteotomy is utilized in isolation and these cartilage defects are not simultaneously addressed with a cartilage restoration procedure.

  • Patella baja is a complicated problem (often involving an atypical biologic response) and should be treated with a continuum of care; tibial tuberosity surgery must have a thorough, scientifically-based role if it is contemplated in that situation.

Although the emphasis of this chapter is on tibial tuberosity surgery and distal realignment for patellofemoral disease, the multifactorial nature of patellofemoral dysfunction requires an acknowledgment that a patellofemoral problem is rarely addressed by a single, isolated surgical treatment. Tibial tuberosity transfer must be examined with a full appreciation of proximal soft tissue balance, limb rotation, and articular cartilage disease (grade, size, and location). Although positive outcomes were initially reported for many distal realignment patellofemoral surgeries, these early positive results often deteriorated markedly with long-term follow-up. In 1938, Hauser first described a distal and medial transfer of the tibial tuberosity. Although patellar stability was established, over time, this led to increased patellofemoral arthrosis secondary to a posteriorization of the patella, thus increasing patellofemoral contact stresses. From these initial results, we learned that TTO must not only address the acute issue but do so without causing intermediate and long-term problems such as chondrosis and arthrosis.

Application of a more scientific and wholistic approach to patellofemoral dysfunction has led to the identification of the importance of the proximal medial patellar restraints (medial patellofemoral ligament, MPFL; medial quadriceps tendon femoral ligament, MQTFL) in preventing lateral patellar instability, the trochlea in normal patellofemoral biomechanics and the role of the lateral retinaculum in serving as a lateral stabilizer. Thus, a focus has been placed on reconstructing the proximal medial patellar restraints when insufficient, addressing trochlear pathoanatomy to ensure smooth patellar entry and gliding in the trochlea, and replacing lateral release with lateral retinacular lengthening to correct patellar tilt and lateral retinaculum contracture. Likewise, the role of TTO for patellofemoral dysfunction continues to evolve both as an isolated procedure and in conjunction with proximal patellofemoral soft tissue surgery and cartilage restoration procedures.

In general, indications for distal realignment surgery of the tibial tuberosity (often in combination with proximal soft tissue stabilization or cartilage restoration procedures) include excessive lateralized tuberosity (elevated TT-TG) or patellar height abnormality (baja or alta) with associated patellofemoral instability, or to unload the patellofemoral compartment in the management of focal articular cartilage defects of the patella and trochlea or isolated patellofemoral arthritis in active patients.

Tibial tuberosity realignment surgeries have gone through a number of iterations and changes over the years. Historically, there have been three large categories of TTO, each with its own initial procedure and associated variations. In 1963, Maquet described an anteriorizing osteotomy to decreased the load in a painful patellofemoral joint. The Roux-Elmslie-Trillat TTO is an isolated tibial tuberosity medialization (TTM) osteotomy to improve stability and correct lateral maltracking. , Finally, the Fulkerson technique focuses on anteromedializing (AMZ) the tibial tuberosity by combining the elements of both the Maquet and Roux-Elmslie-Trillat procedures. ,

Initial tuberosity surgery for treatment of recurrent or chronic patellofemoral instability or maltracking was medialization based on the assumption that the primary pathologic process was an increased quadriceps (Q) angle, while for pain and chondrosis, anteriorization was promoted as the preferred procedure to decrease patellofemoral contact stresses. While repositioning of the distal point of the Q-angle (tibial tuberosity) surgically corrects the pathologic Q-angle, it is important to note that the proximal medial patellar restraints (MPFL and MQTFL) are currently accepted as the main checkreins to lateral patellar instability. Furthermore, the Q-angle, which served as the initial quantifiable measurement for planning of a medialization TTO, has been questioned as an accurate benchmark in light of the poor intraobserver reproducibility of the measurement. However, Merchant et al. recently presented a technique for reliably measuring the Q-angle using a standardized protocol that may be a beneficial addition to the complete patellofemoral evaluation.

From a biomechanics perspective, the initial tuberosity surgeries focused on the action of the various simple force vectors influencing patellar position and motion and the effect of tuberosity position on those vectors. However, this is a complex biomechanical situation, as Imhoff et al. described a number of bony parameters involved in patellofemoral pathology, including femoral and tibial torsion, trochlear dysplasia, elevated TT-TG distance, and coronal axis malalignment in patellofemoral pathology. Dejour et al. emphasized the importance of trochlear morphologic features (i.e., dysplasia) in patients with lateral patellar instability. Others have furthered this initial work by Dejour, demonstrating the biomechanical and clinical effects that the presence and treatment of trochlear dysplasia can have on patellofemoral pathology. The diagnosis and appreciation of femoral (internal) and tibial (external) rotational and angular (valgus) abnormalities are important and the correction of these deformities has demonstrated good outcomes in the management of patients with patellar instability.

In an attempt to objectify tuberosity surgery, we must define normal and abnormal positions of the tuberosity. An objective alternative to the Q angle is the TT-TG distance ( Fig. 103.1 ). The TT-TG distance, as popularized by Dejour et al., quantifies the concept of tibial tuberosity malalignment locally at the knee, providing a reproducible measurement of the lateral pull on the patella. Studies suggest that a TT-TG distance of more than 15 to 20 mm is abnormal; most asymptomatic patients have distances that are less than 15 mm. To exclude the role of tibiofemoral soft tissue rotation and the inability to measure the trochlear groove when none exists (trochlear dysplasia), Seitlinger et al. proposed the TT-PCL measurement, that has been independently verified by others. The upper limit of “normal” for TT-PCL is 24 mm.

Fig. 103.1
Tibial tuberosity to trochlear (femoral) groove distance is measured between perpendicular lines drawn from posterior condyles through the deepest aspect of the trochlea and the midpoint of the patellar tendon attachment of the proximal tibial tuberosity.

Likewise, anteriorization was first shown mathematically to reduce patellofemoral stress, but direct measurement with pressure-sensitive film, real-time pressure transducer arrays, and finite element analysis modeling such as by Cohen and Ateshian show that although stresses are typically reduced with anteriorization, there is a unique response for each knee, and a global 50% force reduction cannot be assumed. More recently, measures of trochlear contact pressures by Rue et al. confirmed the utility of straight anteriorization in reducing patellofemoral contact pressure. Thus, load transfer should play an important role in surgical planning, as opposed to the assumption that there will be an absolute decrease in stress. Medialization improves contact area, while anteriorization decreases the forces; thus, the combination may markedly decrease the patellofemoral stresses as a smaller force is distributed over a larger area. A more recent study demonstrated improved outcomes after anteromedialization TTO in conjunction with MPFL reconstruction, compared to MPFL reconstruction alone in patients with an elevated TT-TG distance of 17 to 20 mm.

With the use of these and other objective parameters, further studies may objectively quantify the preoperative pathologic process to aid in planning of tibial tuberosity surgery.

Preoperative considerations

History

Subgroups considered for tuberosity surgery include patients with static subluxation of the patella, those with patellofemoral chondrosis that requires off-loading of the patellofemoral joint, and those with recurrent lateral instability with significantly elevated TT-TG often combined with other risk factors (i.e., trochlear dysplasia). The history can be highly variable for each subgroup, from the insidious onset of patellofemoral pain to pain that began after patellar instability episodes. Patients with pure instability often only have pain specific to their episodes of instability with little or no pain at baseline, while patients with chondrosis typically have more pain between episodes and effusion. However, there is a great deal of overlap and many of these signs and symptoms do not occur in isolation, as many patients have some combination of the two pathologies. The standard patellofemoral history as outlined by Sherman et al. should be elicited. Functional aspects need to be documented, including the amount of energy needed to cause instability and the degree of stress necessary to cause pain. When relevant, prior surgical operative notes are useful, as are the intraoperative images.

Typical history

  • Failure of an adequate attempt of appropriate physical therapy and bracing

  • Patellofemoral area pain with prolonged flexed knee position, stairs, or squats

  • Giving way with either pain or patellar instability

  • Patellofemoral crepitation, intermittent effusion, and occasional mechanical symptoms

  • Often failed prior chondroplasty and lateral release

Signs and symptoms

Patellofemoral symptoms are ubiquitous but nonetheless must be documented, including functional impairments with respect to pain, crepitation, swelling, giving way, frank patellar instability, and mechanical symptoms associated with a loose body including locking, clicking, catching, or the presence of an effusion. Clinical symptoms coincide with the physical examination findings and include documentation of crepitation during the specific arc of motion, effusion, and patellar laxity and apprehension.

Physical examination

For all patients with patellofemoral dysfunction, a standard examination of the knee along with a core-to-floor examination of the entire functional kinetic chain from the core and pelvis to the foot should be performed. A standard patellofemoral examination should be performed, focusing on the following:

  • Presence of an effusion

  • Location of tenderness to palpation

  • Muscle bulk and strength; specifically, vastus medialis obliquus

  • Knee range of motion

  • Limb rotation (hip and knee internal and external rotation); thigh-foot axis

  • Ligamentous stability

  • Q-angle measurement ; tuberosity position

  • Patellar height (normal, baja, alta)

  • Patellar tracking through knee ROM; evaluation for J-sign

  • Patellar tilt or extent of eversion, especially after prior lateral release

  • Patellar crepitation (document specific angle of flexion)

  • Patellar displacement (measured in quadrants of the trochlea) at varying angles of flexion

  • Apprehension: classic lateral versus global versus medial

  • Flexion angle where apprehension dissipates

  • Fulkerson medial instability test

Imaging

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