15 Rotational osteotomies of the femur and the tibia
1 Introduction and definition
Congenital torsion deformities of the lower extremity may be a consequence of growth disorders of the acetabulum, femur, tibia, or foot and may be the cause of substantial functional limitations and symptoms at the hip, knee, and ankle joints in adolescents and adults [1, 2]. The antetorsion of the acetabular fossa at birth remains to a large extent unchanged during growth ( Fig 15-1a ). Minimal changes may be seen depending on the development of the femoral head. In contrast, the femur and tibia, which are aligned in internal rotation at birth, rotate externally during childhood [3–5]. No further changes in acetabular antetorsion or femoral and tibial rotation are to be expected after the eighth year of life [3–6]. Rotational deformities of the femur may lead to pathological tibial rotation as a form of compensatory overcorrection and thus result in a rotational deformity of the lower extremity at several levels [6–8]. This must be differentiated from posttraumatic rotation deformity.
2 Nomenclature and standard values
The term “torsion” describes the physiological rotation of a bone segment in the longitudinal axis, eg, of long bones such as the femur and tibia. In contrast, the term “rotation” defines rotation between two bone segments and therefore describes relationships at a joint, eg, internal or external rotation of the hip joint.
The torsion angle is defined as the angle of alignment of the distal joint axis in relation to the alignment of the proximal joint in the transverse plane (internal and external rotation). Standard values and standard deviations were originally based on examination of anatomical cross sections and clinical studies [5, 9], but now more precise values have been obtained by computed tomography [4, 10–12]. Standard values differ across different ethnic groups, eg, Asians compared with West Europeans .
The torsion angle of the femur is the angle between the line drawn from the center of the femoral head in the transverse plane centrally through the femoral neck and the tangent at the posterior femoral condyles (see Fig 15-1b ).
In relation to the distal part of the femoral shaft, the femoral neck is positioned in physiological external rotation, so-called antetorsion. The torsion angle of the femur between the distal femoral condyles and the femoral neck in adults is normally 15.6 ± 6.7° [4, 12]. The torsion angle of the tibia is the angle between the posterior tangents at the proximal tibial condyles and the central distal transmalleolar axis (see Fig 15-1c ). The standard value for the tibial external torsion angle at the end of growth is 23.5 ± 5.1° [4, 12]. By definition, pathological torsion is present if the angle measured differs more than two standard deviations from the norm .
Congenital torsion deformities can lead to serious symptoms and cause functional limitations of all joints of the lower extremity in adolescence and adulthood. Pathological antetorsion as well as femoral retrotorsion can lead to premature coxarthrosis [9, 11]. Unphysiological femoral internal or antetorsion leads to instability of the hip joint, especially if combined with increased antetorsion of the acetabulum . The joint most frequently affected is the knee since it has very little ability for rotatory compensation compared with the hip or upper ankle joint [6, 7, 9–11, 14, 15]. Torsional malalignment of the femur can result in increased patella contact pressure with secondary retropatellar cartilage damage or retropatellar joint degeneration or patellofemoral malalignment with instability of the patella, subluxation, or dislocation of the patella [2, 6, 7, 9, 16, 17]. Evidence of an increased incidence of pathological antetorsion of the femur and internal torsional malalignment of the tibia has been found in patients with tibiofemoral joint degeneration . Torsion deformity of the leg affects gait pattern and heel-to-toe weight bearing and can lead to arthrotic alterations due to unphysiological load distribution at the upper ankle joint and foot .
Torsion = physiological rotation of a bone segment in the longitudinal axis.
Rotation = rotation between two bone segments, ie, joint motion.
Torsion angle = angle of alignment of the distal joint axis of a long bone in relation to the alignment of the proximal joint in the transverse plane.
Physiological femoral torsion angle = 15.6 ± 6.7°.
Physiological tibial torsion angle = 23.5 ± 5.1°.
Pathological torsion exists if the angle measured deviates more than two standard deviations from the norm.
3 Preoperative diagnostics
3.1 Clinical examination
Clinical examination must evaluate the alignment of the lower extremity in both the frontal and sagittal planes. Particular attention must be paid to the alignment of the patellae and the position of the feet. Physiologically, the feet and patellae point straight forward. A medialized patella, valgus weight-bearing axis, or internal rotation deformity of the feet may indicate increased internal torsion of the femur, so-called coxa antetorta. Similarly, a lateralized patella, varus weight-bearing axis, or external rotation deformity of the feet may indicate femoral retrotorsion or coxa retrotorta. Manifestation of a medially aligned patella combined with external rotation of the feet is defined as torsion malalignment syndrome. Its cause is pathological antetorsion of the femur that leads to secondary compensatory external torsion of the tibia .
The assessment protocol (rotational profile) designed by Staheli is well suited to determine the exact location and extent of a deformity [4, 5]. First, the gait pattern is analyzed and the rotational alignment of the foot is assessed. The forefoot is normally positioned in 10–35° external rotation at the moment of touchdown ( Fig 15-2a ). Next, the internal and external rotation capabilities at the hip are analyzed with the patient in the prone position ( Fig 15-2b ). According to the Neutral-0 Method, internal rotation of 45° and external rotation of 30° are possible, whereby attention must be paid to side-to-side differences. The angle between the foot axis and a straight line through the thigh is measured with the patient in the prone position, the knee in 90° flexion, and the upper ankle joint in the neutral position (norm: 10–30°) ( Fig 15-2c ). Here, the focus is on lower leg torsion although possible foot deformities (eg, crescent-like feet, club-foot) must be taken into account too.
3.2 Diagnostic imaging
Radiological diagnostics include conventional radiographic views of the femur and tibia in both planes. If the cause of torsion deformity is probably in the region of the proximal femur or acetabulum, a pelvic overview is required in order to measure the CE angle (Wiberg angle, ie, center of the femoral head to end of acetabular roof) and the CCD angle (caput collum diaphyseal angle). Mathematical formulae can be applied to diagnose femoral and tibial torsion from conventional x-rays [7, 17]. Axial computed tomography (CT) will, however, simplify precise measurement of these angles. Imaging is performed with the patient in the supine position with the legs parallel. Scans are obtained at the level of the acetabulum with femoral head and neck, at the femoral condyles, at the tibial condyles, and at the level of the ankle joint. The method for obtaining the torsion angles is illustrated in Fig 15-1a-c . To assess patellofemoral joint alignment, the two scans showing the lowest point of the trochlea (trochlear groove, TG) and the most anterior point of the tibial tuberosity (TT) are projected onto each other ( Fig 15-3 ). The distance between these two points is normally 10-15 mm , and is often pathologically enlarged or reduced in congenital torsion deformities with abnormal patellofemoral alignment as a consequence .
4 Patient selection
Isolated torsion deformities of the leg without clinical symptoms do not require correction. If there are clinical signs but pathological torsion is only slight (up to two standard deviations from the norm on the CT scans), conservative treatment with corrective insoles and physiotherapeutic muscle strengthening exercises (eg, isometric quadriceps exercises) is usually successful. If the measured torsion angle exceeds two standard deviations from the norm, rotational osteotomy is indicated  ( Table 15-1 ). Correction should be performed at the level of the deformity since compensatory rotational osteotomy at an unaffected site will only make the deformity more complex.
Indication for surgery
> 25° or < −15°
Femoral torsion angle
15.6 ± 6.7°
> 30° or < 0°
Tibial torsion angle
23 ± 5.1°
> 35° or < 10°
5 General surgical technique
5.1 Osteotomy technique
The osteotomy techniques presented here aim to correct the deformity by a one-stage correction osteotomy. Multidimensional and gradual corrections with application of external fixation systems (unilateral fixator, ring fixator; [4, 17, 19]) are not the subject of this chapter. Osteotomy techniques depend on the planned fixation method. Percutaneous drill osteotomy or the use of a Gigli saw through a mini skin incision is appropriate for an intramedullary nail or external fixator . Application of an intramedullary saw followed by intramedullary nail fixation can be used for osteotomy of the diaphysis of the long bones . Osteotomy with the oscillating saw permits better visualization of the osteotomy plane but requires a more invasive approach and may lead to heat-induced bone necrosis.
5.2 Osteotomy level
In the treatment of congenital torsion deformities of the femur, derotation should be performed in the intertrochanteric region with an angled blade plate because of the simplicity of the approach, the excellent growth and healing potential of the metaphyseal zone, and the good fixation options. If correction in the diaphyseal or distal regions of the femur is required, osteosynthesis by intramedullary nail, angled blade plate or fixed-angle plate fixator is preferred. It is important to remember that the bone consolidation phase is longer in the diaphyseal part compared with the proximal part of the femur. Higher complication rates are reported in the literature for diaphyseal and distal femoral osteotomies [2, 20].
The proximal tibia can be osteotomized inferior or superior to the tibial tuberosity. Good bone healing can be assumed for a saw cut in the metaphyseal zone above the tuberosity, but it leaves little room for stable fixation in the proximal segment ( Fig 15-4a ). The disadvantage of an osteotomy below the tuberosity ( Fig 15-4b ) is poorer bone consolidation, but it does permit secure fixation of the proximal segment. Therefore, the authors recommend a transverse saw cut at the level of the tibial tuberosity as this will ensure good healing potential combined with stable fixation. The tuberosity can be left intact by making an anterior saw cut ascending cranially behind the tuberosity ( Fig 15-4c ) or a descending oblique cut ( Fig 15-4d ). In the latter technique a lag screw is used to prevent avulsion fracture due to the forces exerted by the patellar tendon. If a transverse osteotomy at the level of the tuberosity is combined with a separate tuberosity osteotomy ( Fig 15-4e ) two or three lag screws are recommended for tuberosity fixation.
Osteotomies above the tuberosity must take into account the fact that rotation of the distal segment leads to medial or lateral translation of the tuberosity. The extent of translation can be determined by tracing it from the CT images or by mathematical calculation using the formula given in Fig 15-5 . Physiological retropatellar and femoral cartilage loading and stable patellar tracking is guaranteed if the tuberosity is positioned 10–15 mm lateral to the mid-trochlea (so-called tibial tuberosity trochlea distance, TT-TG, see above) . Rotational osteotomy below the tuberosity is not a problem since the tuberosity remains on the proximal segment and the distance to the femoral trochlea thus remains unchanged after rotation correction of the distal segment . If it becomes apparent during preoperative planning that the rotational osteotomy will lead to a pathologically increased or decreased TT-TG distance, an alternative osteotomy level or a separate tuberosity osteotomy with appropriate lateral or medial translation of the tuberosity should be considered.
Due to the good bone healing potential, distal tibial rotational osteotomies should be positioned in the metaphyseal region above the tibiofibular syndesmosis. Rotation in the diaphyseal region may cause incongruence and clinical symptoms due to the triangular cross section of the tibial shaft.
Growth and healing potential in the metaphyseal zone of the long bones is excellent, whereas the diaphyseal region has a longer bone consolidation time.
Tibial osteotomy above the tuberosity leads to medial or lateral translation of the tuberosity after distal segment rotation.
If a rotational osteotomy results in pathological increase or decrease of the TT-TG distance, an alternative osteotomy site or a separate osteotomy with appropriate lateral or medial tuberosity translation should be considered.
5.3 Soft-tissue problems and neurovascular structures
Depending on the level of the osteotomy, rotational osteotomy of the femur may have an important effect on the position and the direction of pull of the quadriceps femoris muscle group. By contrast, proximal tibial rotational osteotomies only have a minimal effect on the function of the lower leg muscles. Although diaphyseal and distal torsional changes of the tibia may cause twisting and elongation of the muscle compartments or a change in direction of pull of the tendons, functional limitations have not been reported as long as the correction angle is less than 45° .
Special attention must be paid to the neurovascular structures if more extensive torsional correction is required. Tension and compression during internal rotational osteotomy of the femur may damage the sciatic nerve. By contrast, external rotational osteotomies present no difficulties in this respect.
Since the peroneal nerve runs around the fibula, increased internal torsion of the proximal tibia during internal rotational osteotomy may result in overextension of the nerve or entrapment in the intercompartmental septum between the anterior and lateral muscle compartments. The peroneal nerve may be damaged during external rotational osteotomy due to compression within the septum or due to tension in the anterior compartmental fasciae . This problem can be avoided by careful decompression of the nerve or by performing diaphyseal or distal derotation where the correction angle is greater than 20°.
Distal external rotational osteotomy of the tibia may cause overextension of the posterior tibial nerve within the posterior compartmental fasciae of the lower leg and tension in the fasciae of the abductor hallucis in the tarsal tunnel . These complications can be prevented by release of both fasciae in the tarsal tunnel.
If more than a 20° rotational correction of the tibia is planned, careful decompression of the peroneal nerve is essential in proximal tibial rotational osteotomies or, alternatively, a diaphyseal or distal derotation site should be chosen. In any case, intra compartmental decompression by fasciotomy is recommended.