Proximal Femur Rotational Osteotomy
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Proximal Femur Rotational Osteotomy
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.
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: 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
noted a significantly increased association of internal femoral torsion with patellar instability and chondropathy.
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.
TABLE 34.1 Indications and Contraindications for Proximal Femoral Derotational Osteotomy
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
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)
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