Since its introduction in 1965 [19], PFVO has become an established surgical treatment approach for LCPD [20]. By producing increased varus angulation of the proximal femur, the femoral head is centred within the acetabulum [21]. To further improve containment the proximal femur may additionally be altered in the sagittal and transverse plane through modifications of the osteotomy [22]. The aim is to shift the fragile capital femoral epiphysis out of the main load zone [22]. The load-relieving effect may ultimately improve remodelling of the biologically plastic femoral head during the healing or revascularization phase [21, 22]. Moreover, relocation of the femoral head through PFVO does not influence the acetabular centre of rotation, as is the case in pelvic osteotomies. Thus, an increase of the intraarticular pressure and further impairment of the blood supply to the femoral head can be avoided [23].
PFVO has shown to achieve radiographic results – in particular regarding the Stulberg classification – superior to those of patients undergoing non-operative treatment [20]. Nonetheless, correct indication and timing of PFVO are crucial to achieve a satisfactory outcome. Containment should be re-established before onset of re-ossification of the femoral head [24]. If conducted in a timely manner, PFVO may help to shorten the fragmentation phase, and femoral head deformation may be less severe due to the reduced lateral subluxation of the femoral head [5, 24]. Ideally, the spherical shape of the femoral head can be preserved. In particular patients older than six years of age should be considered for surgical treatment, as the ability of the femoral head to spontaneously remodel seems to remarkably decrease beyond this age [25]. This patient group also appears to benefit more from PFVO than non-operative treatment [5, 21].
Even though PFVO has been reported to be beneficial to the healing process if indication, timing and technique are executed appropriately, it is also associated with certain pitfalls and disadvantages. For instance, preservation of the medial femoral circumflex artery is of utmost significance to maintain sufficient blood supply to the proximal femur and prevent further damage [10]. Furthermore, overcorrection of varus angulation may shift part of the femoral neck into the main load zone, resulting in incorrect load distribution which may impair healing of the capital femoral epiphysis in a spherical shape [22]. It is generally recommended to not produce a varus angulation of less than 100° [26, 27]. However, even moderate varization of the proximal femur will inevitably produce an elevation of the tip of the greater trochanter relative to the centre of rotation of the femoral head. An overriding greater trochanter, in turn, results in shortening of the origin to insertion length and a reduced lever arm of the hip abductor muscles [28]. The decreased resting length and abductor lever arm ratio may lead to a functional insufficiency of the hip abductors [29]. Owed to this, Trendelenburg gait as well as fatigue pain on walking are frequently observed after PFVO and may persist permanently [30]. Moreover, an overriding greater trochanter may also cause painful pelvitrochanteric impingement, further limiting hip joint mobility [31].
Combining PFVO with a modified trochanteric flip osteotomy to distalize the greater trochanter addresses these issues by reestablishing the original resting length and lever arm, thus maintaining hip abductor strength. The necessity of subsequent surgeries may hence be avoided by preserving or improving hip function, pain, and gait. The principle and rationale of the PFVO with trochanter distalization for treatment of LCPD was first presented by Birke et al. at the EPOS meeting 2016 [32]. Birke combined a trochanter flip approach and development of the retinacular soft tissue flap with a novel release cut technique to achieve varization with the necessary medialisation of the femoral shaft. He utilized a 130 degree cannulated blade plate allowing sufficient bone stock for refixation of the distalised greater trochanter, which was fixated at the lateral aspect of the plate. We modified this technique by employing a 90 or 100 degree rather than a 130 degree blade plate, which allows threading the greater trochanter with the blade and fixating it to the femoral neck. However, since the threaded greater trochanter impedes sufficient medialization through the blade offset, a recess cut is still required to avoid lateral translation of the distal fragment. Even though radiologically, adequate distalization of the greater trochanter was observed after PFVO with a modified trochanter flip osteotomy, we nevertheless observed persistent Trendelenburg gait in two patients. This may be ought to the fact that we performed only moderate lateralization of the greater trochanter. However, apart from height of the greater trochanter, an adequate distance between the centre of the femoral head and the tip of the greater trochanter also plays an important role regarding the effectiveness of abductor muscle strength, since the pelvitrochanteric muscles require less force to maintain the pelvis level during the single stance phase [33]. In LCPD, enlargement of the femoral head is frequently observed, thus reducing the centre head-trochanteric distance. This may lead to weakening of hip abductor muscle strength, even if the greater trochanter has been sufficiently distalized [29]. In patients preoperatively presenting an enlarged femoral head and Trendelenburg gait, more aggressive lateralization of the greater trochanter should thus be considered to improve hip abductor strength. Alternatively, a femoral neck lengthening osteotomy has been declared effective to achieve this goal, while concomitantly decreasing leg length discrepancy [29]. However, it should be noted that femoral neck lengthening osteotomy inevitably increases the intraarticular pressure and may thus aggravate deformation of the femoral head in LCPD. Apophyseodesis of the greater trochanter has been proposed as another alternative approach to PFVO to prevent an overriding greater trochanter and, consecutively, Trendelenburg gait [10]. This procedure may also avoid iatrogenic varus deformity [34]. However, it has been constituted that this measure only renders effective if performed before eight years of age and if Trendelenburg gait has not yet established [35, 36]. Apart of age at surgery, it appears that the size of the femoral head at healing significantly influences the effectiveness of apophyseodesis of the greater trochanter [37], thus further limiting its applicability. We thus believe that in patients in whom this technique is not applicable, PFVO combined with a modified trochanter flip osteotomy is an efficient procedure to restore the physiological position of the greater trochanter and hence improve hip containment, while showing an improved biomechanical outcome compared to traditional osteotomy techniques. Even though we observed an unsatisfactory radiological outcome with Stulberg Class V hip in one patient patients of the studied cohort at the time of last follow-up, it should be noted that this patient showed Herring class C preoperatively, which reportedly is associated with a poorer treatment outcome, irrespective of age at and choice of treatment [21]. Moreover, the pathogenesis of LCPD is immensely complex and it may thus not always be sufficient to solely modify biomechanical factors [5].