Surgical Considerations for Tibial Tubercle Osteotomy
Jason Koh
INTRODUCTION
Pathogenesis
Patellofemoral disorders are common in the general population and a frequent cause for orthopedic consultation.
Patellofemoral pain has been reported in up to 30% of students aged 13 to 19 years, resulting in limitations of athletic activity in up to 74% of these patients.1
Chondral lesions of the patellofemoral joint are common and have been reported in 60% of more than 25 000 patients who underwent knee arthroscopic surgeries.1
Patellofemoral instability is also common, with an estimated incidence of patellofemoral dislocations of 5.8 per 100 000, increasing to 29 per 100 000 in the 10- to 17-year age group.1
The recurrence rate of patellar instability after nonoperative treatment ranges from 15% to 44%, and surgical intervention is often required.1
Anatomy
The function of the patellofemoral joint is normally maintained by a complex interaction between soft tissues and bony structures.
The anatomic structures that stabilize the patella can be divided into three groups.
First are the active stabilizers, which are the components of the quadriceps femoris. The quadriceps tendon, which inserts onto the superior pole of the patella, is formed by the convergence of the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius muscles approximately 5 to 8 cm proximal to the superior pole of the patella. The patellar tendon originates from the inferior pole of the patella and inserts onto the tibial tuberosity, which is lateral to the midline of the tibia. The mean width of the patellar tendon is 24 to 33 mm, and the mean length is 4.7 cm.1
Second is the passive stability, which is provided by the medial retinaculum including the medial patellofemoral ligament (MPFL). The MPFL, a thickening of the medial retinaculum, extends from a point between the adductor tubercle and the medial epicondyle to the proximal and medial surface of the patella and is a biomechanically important restraint to lateral patellar subluxation. The MPFL is responsible for 50% to 60% of the medial stability afforded to the patella during the first 30° of flexion and is crucial for the maintenance of patellar stability. MPFL tearing occurs with almost all patellar dislocations, and the MPFL’s resultant patholaxity is a frequent contributor to recurrent lateral patellar instability.1
Third are the bony anatomy and morphology of the patellofemoral joint, which provide static stability. Variations in bone morphology include trochlear dysplasia, patella alta, and an abnormal lateral position of the tibial tuberosity.2,3
Patellofemoral pain is usually caused by patellar malalignment and associated articular cartilage lesions. Malalignment of the extensor mechanism results in lateral maltracking of the patella, or objective patellar instability, and can lead to subsequent cartilage injury.4,5,6
More than 100 procedures have been described for the treatment of the patellofemoral syndrome, and many of these procedures are designed to realign the patella and normalize the contact pressures in an attempt to relieve pain.6,7
Malalignment can be corrected with multiple procedures, including lateral release, medial retinacular reefing, MPFL reconstruction, trochleoplasty, and transfer of the tibial tubercle.
Patellofemoral pain associated with patellar maltracking and lateral instability is often considered an indication for tibial tubercle transfer. When there is little or no articular damage, tibial tubercle medialization, such as the Elmslie-Trillat procedure, may be the most appropriate.8,9
Most patients, however, have articular cartilage lesions at the distal medial or central lateral patellar facets as a result of a long-standing malalignment. In such cases, a Fulkerson tibial tubercle anteromedialization (AMZ) is advised.
AMZ will help to unload the distal and lateral facets of the patella while improving the extensor mechanism.5,10 A successful outcome from AMZ requires some preservation of the medial and proximal articular cartilage of the patella. Because this procedure moves the tibial tubercle medially and anteriorly, loads are transferred onto the proximal and medial patellar facets. If this area is damaged, a tibial tubercle transfer is less likely to be successful.
Classification/Types of Tibial Tubercle Osteotomy
Various types of tibial tubercle osteotomy (TTO) have been described in the literature; many of which are historical in nature.
The two most frequently used osteotomies are the medialization osteotomy (Elmslie-Trillat) and AMZ osteotomy (Fulkerson). Several surgical modifications of these techniques have been described in the literature (Figure 14.1).
Medialization (Elmslie-Trillat)
Indications
Patellar instability with lateralization of tibial tubercle
Ideal patient who has good quadriceps strength is physically active and is committed to adherence to the postoperative rehabilitation protocol.
If there is articular cartilage damage, it is primarily located on the lateral patella or lateral trochlea.
The osteotomy can unload these areas, creating a favorable mechanical environment.
Contraindications
Most contraindications are relative.
Neuromuscular lack of quadriceps control.
Anatomically “normal” extensor mechanism alignment
Diffuse or medial chondral lesions
Figure 14.1 The plane of osteotomy for common tibial tubercle osteotomies. A, Anteromedialization (Fulkerson). The slope can vary based on the planned amount of medialization and anteriorization. B, Medialization (Elmslie-Trillat). C, Modified Elmslie-Trillat osteotomy. A trapezoid bone fragment is produced by an oblique (45°) lateral cut to reach cancellous bone and a horizontal medial cut to allow for straight medialization. T, tibia; F, fibula.
Reported instability that is not consistent with physical examination or is not consistent with patellar instability
Inflammatory arthritis
Posteromedialization (Hauser) is not used because of increased rates of patellofemoral arthrosis.
Anteriorization (Maquet)
Indicated for distal pole lesions
Risk of skin necrosis if tubercle is elevated greater than 2 cm.
AMZ (Fulkerson) is discussed in detail in Chapter 15.
Table 14.1 lists indications and contraindications for tibial tubercle osteotomy.
EVALUATION
Patient History
An accurate clinical evaluation of patients with patellofemoral disorders is the cornerstone of effective treatment. With careful history taking, the surgeon should understand the origin of the pain and delineate where the pain occurs in the flexion arc of the knee. These will be useful in locating a specific articular lesion.
The history should elicit the location (diffuse anterior vs lateral facet), duration (acute vs chronic), and onset (traumatic vs insidious) of symptoms.
Details regarding prior instability events, including number of events, severity (frank dislocation vs subluxation), mechanism of injury (sport vs uneven ground), and need for reduction maneuvers, should be documented.
Prior nonoperative treatment (nonsteroidal anti-inflammatory drugs [NSAIDs], injections, physical therapy, and bracing) and surgical reports should be reviewed.
Patient-specific variables such as age, body mass index, physical fitness, and emotional status (ie, expectations, motivations) are important prognostic indicators and may influence patient selection for TTO procedures.
Patients should also be asked about potential contraindications to TTO, including smoking or ability to comply with the postoperative rehabilitation regimen.1
TABLE 14.1 Indications and Contraindications for Tibial Tubercle Osteotomy | ||||
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Physical Examination and Findings
Suggested physical examinations for patients suspected of having patellofemoral disorders include evaluating lower extremity alignment, gait pattern, patellar mobility (patellar tilt and medial and lateral glides), patellar tracking (J-sign), the apprehension test, soft-tissue tenderness, the patellar grind test, and musculature flexibility.11
The J-sign evaluates patellar tracking by demonstrating lateral deviation of the patella as the knee moves from flexion to full extension. A positive J-sign is suggestive of possible underlying bony alignment issues, laxity or atrophy of the medial soft-tissue restraints, tightness of the lateral structures, or some combination of the above abnormalities.
The patellar apprehension test is performed with the patient supine and the knee extended and the quadriceps relaxed. The examiner then attempts to passively displace the patella laterally. Asymmetric painful laxity, apprehension, and/or involuntary contraction of the patient’s quadriceps muscle (ie, guarding) to avoid a dislocation signify a positive test result for patellofemoral instability.
Imaging
After a complete history and a physical examination, plain radiographs in the anteroposterior, lateral, and axial views are obtained.
A lateral radiograph taken with 30° of knee flexion will reveal whether there is patella alta or patella baja. In addition, patellar tilt and trochlear dysplasia of the most proximal part of the trochlea are best noted on the true lateral radiograph, with the knee in extension.12,13
On the Merchant axial radiograph, patellar subluxation and tilt are assessed by the congruence angle and the tilt angle, respectively.
Computed tomography (CT) of the patellofemoral joint with the knee in 15°, 30°, and 45° of flexion can provide valuable objective information regarding subtle abnormalities of patellar alignment.5
CT can be used to superimpose the images of trochlea and tuberosity to measure the tibial tubercle-trochlear groove (TT-TG) distance. The deepest point of the TG and the highest point of the TT are projected perpendicularly on the line tangential to the posterior condyle. The distance between these points is defined as the TT-TG distance.14 The TT-TG distance has been shown to be greater than 20 mm in 56% of individuals with a history of patellar dislocation compared with a mean of 12 mm in a control group.13,14 Measurements greater than 20 mm are considered abnormal, and TT-TG distance should be decreased surgically to 10 to 14 mm.15
Magnetic resonance imaging (MRI) provides very useful information for preoperative planning, including the assessment of articular cartilage lesions. Because there is a difference between the osseous and cartilaginous contours of the patella, MRI gives a more accurate picture of the patellofemoral congruence than CT.
MRI offers superior definition of cartilage as well as soft tissue. It can identify osseous contusions or edema patterns after patellar dislocations, osteochondral fragment avulsions, injuries to the MPFL and vastus medialis obliquus, and joint effusion. In addition, MRI is 85% sensitive and 70% accurate in detecting MPFL tears.1
TT-TG distance can be determined reliably on MRI using either cartilage or bony landmarks.16 Using above parameters of TT-TG distance and the location and severity of associated articular cartilage lesions, the desired amount of anteromedial transfer and the angle of osteotomy can be determined preoperatively.Related posts:
Surgical Considerations During Patellar Stabilization
Quadricepsplasty Techniques for Patellar Stabilization
Lateral Retinacular Release and Lengthening
Chondral Lesions and Patellar Instability
Proximal Femur Rotational Osteotomy
Failed Medial Patellofemoral Ligament Reconstruction: Causes and Treatment
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