Proximal Femur Rotational Osteotomy
Todd J. Frush
INTRODUCTION
Pathogenesis
The lateral displacement forces upon the patella increase with inward twisting of the knee. These forces may cause patellofemoral (PF) ligament failure, subluxation, dislocation, or cartilage injury (Figure 34.1). Anterior knee pain is a common manifestation of the abnormal forces.
If the trochlear groove is deficient from dysplasia, then the risk of medial PF ligament failure is increased with rotational malalignment. This can result in patellar dislocation or subluxation. However, if the bony restraints are sufficient to counteract the increased forces upon the PF joint, the ligaments may not fail. The result will likely be increased contact pressures upon the articular cartilage, leading to PF chondromalacia or arthrosis.1
Alterations in both femoral and tibial torsion change the effective lever arm of the hip stabilizers2 and may account for the frequency of soft-tissue complaints around the hip and pelvis, as well as the increased pelvic tilt and lumbar lordosis seen in these patients. Examples of the change in position of the hip and knee with a constant foot progression angle and changes in femoral and tibial torsion are illustrated in Chapter 32.
There exists biomechanical evidence of the effects of rotational malalignment of the femur upon the PF joint. Lee et al1 used a cadaveric model to show that PF contact pressures increased at 20° of rotational deformity. This was not a linear increase, and therefore, there was a considerable change in the contact pressures when the malrotation increased to 30°.
For internal rotation deformity of the femur, the increased contact pressures were along the lateral patellar facet.
Fujikawa et al3 did a biomechanical study that measured PF contact pressures and concluded that if an angular deformity and a torsional deformity coexist, the rotatory component causes the greater PF changes.
Figure 34.1 A, A balanced tension upon the retinaculum and patellofemoral ligaments and balanced compression upon the articular cartilage in a normally aligned knee. B, With inward twisting of the knee, the medial soft-tissue tension and lateral patellofemoral articular cartilage pressure increases. This can lead to instability or articular cartilage damage. Reprinted from Noyes FR. Knee Disorders: Surgery, Rehabilitation, Clinical Outcomes. 2nd ed. Philadelphia, PA: Elsevier; 2010 with permission.
Figure 34.2 Illustration showing the relevant axis points of the proximal femur for measurement of femoral rotation. From Kaiser P, Attal R, Kammerer M, et al. Significant differences in femoral torsion values depending on the CT measurement technique. Arch Orthop Trauma Surg. 2016;136(9):1259-1264. Also available at: http://creativecommons.org/licenses/by/4.0/. Accessed December 15, 2017.
From a clinical standpoint, there is ample evidence suggesting that rotational malalignment of the femur results in PF symptoms.
Takai et al4 measured femoral and tibial rotation in patients with unicompartmental arthritis and found that the highest correlation was with PF arthritis. They found an increased association with femoral anteversion (23° in the PF osteoarthritis group vs. 9° in the control group).
Lerat et al5,6 noted a significantly increased association of internal femoral torsion with patellar instability and chondropathy.
Janssen7 found a high correlation between PF instability and an increase in medial femoral torsion and speculated that medial femoral torsion was also responsible for the development of trochlear dysplasia.
Stroud et al8 followed 92 patients who at age 5 showed 30° greater medial hip rotation (measured in extension) than lateral rotation. At age 24, PF pain was noted by 30% in the increased medial rotation group compared with only 8% in the control group.
Of perhaps great significance to those who believe that muscle strengthening is the key to treating PF symptoms, Nyland et al9 found a significant decrease in vastus medialis and gluteus medius electromyogram amplitude in athletes with clinically increased internal femoral torsion.
Arnold et al2 noted that an increase in femoral anteversion of 30° to 40° and decreased abduction moment arm strength of 40% to 50% was enough to impair normal walking, and therefore, those individuals required turning the knee inward to keep the hip from collapsing.
Torsional Measurements
Rotational assessment may be made with either computed tomography (CT) scan or magnetic resonance imaging; however, CT scan is preferred owing to better visualization of the bony anatomy.
Many techniques for assessment of rotational alignment have been described. A recent study by Kaiser et al10 compared six different measurement techniques in 52 human cadaveric femurs (Figure 34.2). The study found that all six of these measurement techniques had good intra- and interobserver reliability and that they all compared well to each measurement’s published normative values. The variability from one study to another was more than 11°, and therefore, it is very important to be aware of the normal values for the particular measurement technique that is used.
Our preferred technique was described by Murphy et al.11 The proximal axis utilizes a line on superimposed CT cuts through the center of the femoral head and the base of the femoral neck where the circular nature of the femoral shaft becomes apparent. The distal axis is a line along the posterior condyles of the distal femur.
Table 34.1 lists indications and contraindications for proximal femoral derotational osteotomy.
TABLE 34.1 Indications and Contraindications for Proximal Femoral Derotational Osteotomy | ||||
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Indications
There are many anatomic variations and factors that may contribute to PF pain, arthrosis, and instability. These include trochlea dysplasia, rotational and coronal malalignment, patella alta, hypermobility syndromes, soft-tissue deficiency, direct trauma, and iatrogenic causes. Each of these must be assessed for their relative contribution to the overall condition.
The goal is to fix the primary pathology and symptoms with (1) anatomic correction and (2) address factors that will accomplish this with the least amount of surgery. The second point is important because oftentimes these patients have multiple risk factors for their instability or arthrosis. If the goal were to be to correct all of these, scar tissue, long-term stiffness, and persistent weakness may be the result.
If there is less than 20° of malrotation, there may be some contribution to the PF pathology. In Takai et al’s study,4 14° of malrotation correlated with PF arthrosis. In Lee’s study,1 however, the PF contact pressures did not show a statistically significant increase in a cadaveric model until the malrotation was 30° or more. Therefore, I suggest that if there are PF symptoms associated with malrotation exceeding 30°, then rotational osteotomy may be indicated.
It is important to note that proximal femoral rotational osteotomy changes the displacement forces upon the patella, although it does not directly alter the soft-tissue restraints.
SURGICAL TECHNIQUE
For isolated femoral malalignment in the transverse plane, the osteotomy can be performed anywhere between the reference points proximally and distally. The author prefers to perform the osteotomy at the proximal aspect of the femur because it avoids damage and scarring to the distal quadriceps. In addition, it avoids creating bony prominences distally when rotating the bone where it resembles a trapezoid.
If there is malalignment present in the coronal plane that must be addressed concurrent to the transverse plane correction, it is preferable to do the osteotomy distally at the supracondylar portion of the femur.
Nail Versus Plate
Proximal femoral rotational osteotomies may be stabilized with either an intramedullary nail (IMN) or a plate and screws. Although many recent studies of osteotomies of this type utilized an IMN,12,13 there is a lack of evidence supporting one technique over the other. Teitge14 has performed many of these osteotomies with an IMN in his 1980s series; however, there are several reasons to consider fixation with a plate and screws instead. First, the IMN is a load-sharing device, resulting in secondary bone healing, rather than the desired primary bone healing seen with compression from plate/screws. The rate of union with an IMN may be slower; thus, a delayed union may be a factor (Figure 34.3).Related posts:
Surgical Considerations During Patellar Stabilization
Quadricepsplasty Techniques for Patellar Stabilization
Tibial Tubercle Distalization
Open Proximal Trochleoplasty (Grooveplasty)
Overmedialization Following Tibial Tuberosity Osteotomy
Failed Medial Patellofemoral Ligament Reconstruction: Causes and Treatment
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