Articular hip distraction can be applied either by using a monolateral articulated distractor or a circular fixator. The fixator should be aligned such that its axis is aligned with the transverse axis of the hip joint. Following distraction, the range of motion is maintained with regular physiotherapy. It is a useful salvage procedure in older children with hip stiffness, when other methods of containment are not applicable.
Articulated distraction or arthrodiatasis is a new method of treatment of Legg-Calvé-Perthes disease (LCPD). The term arthrodiatasis is derived from the Greek words arthro (joint), dia (through), and taxis (to stretch out). The method has been used to treat a variety of hip conditions, such as avascular necrosis, osteoarthritis, chondrolysis, neglected hip dislocation, unstable capital femoral epiphysis, and the adolescent arthritic hip.
Rationale
The aim of treatment of LCPD is to prevent the residual hip deformity, which can lead to early degenerative arthritis. During the stage of revascularization, the bone of the femoral head is biologically weak. When this weak bone is subjected to weight-bearing stresses across the edge of the acetabulum, the femoral head can become irreversibly deformed. Even when the hip is not bearing weight, muscular contraction can generate forces across the joint that may exceed the body weight; these forces can cause the femoral head to deform. Joint distraction attempts to neutralize muscular and weight-bearing forces on the femoral epiphysis, induce neovascularization, and prevent femoral head deformation.
One advantage of distraction is that it does not change the anatomy of the proximal femur. Besides, it can be employed even when the hip is very stiff, when other methods of surgical containment are contraindicated.
Methods
Articulated hip distraction can be applied with either a monolateral fixator or a circular external fixator. If fixed adduction or flexion deformities are present, tenotomies of the adductors and the psoas tendons are first performed.
Whatever the type of external fixator, it should be aligned such that its rotating axis is in line with the flexion–extension axis of the hip joint. This step is crucial. If alignment of the center of rotation is not accurate, limitation of movement and even painful loosening of the pins may occur. A guidewire is inserted from the lateral side through the center of rotation of the hip joint under image-intensifier control while the lower limb is kept in 15° abduction, neutral rotation, and 0° flexion. This position is used so that the guidewire is perpendicular to the femoral shaft. The hinge of the monolateral articulated distraction device is aligned with this guidewire ( Fig. 1 ). Two half pins (5 or 6 mm) are inserted in the supra-acetabular area using the image intensifier for avoiding too-deep penetration. The author prefers the use of hydroxyapatite-coated pins. Another 2 or 3 pins are applied to the shaft of the femur in the midsagittal plane. The guide pin is removed and the range of motion of the hip is checked. A circular external fixator can be applied with the same principles as the monolateral hinged fixator. Schanz pins are introduced in a convergent manner into the iliac crest, the supra-acetabular area, or both, and fixed to a pelvic arch. Another arch or a complete ring is applied to the femur by wires or pins. The connection between the two parts is built using rods and hinges, ensuring that the level of the hinge is at the center of hip rotation as previously described. In cases with flexion hip deformity, an extension rod can be applied for a temporary period to correct the deformity and restrict all movements.
Methods
Articulated hip distraction can be applied with either a monolateral fixator or a circular external fixator. If fixed adduction or flexion deformities are present, tenotomies of the adductors and the psoas tendons are first performed.
Whatever the type of external fixator, it should be aligned such that its rotating axis is in line with the flexion–extension axis of the hip joint. This step is crucial. If alignment of the center of rotation is not accurate, limitation of movement and even painful loosening of the pins may occur. A guidewire is inserted from the lateral side through the center of rotation of the hip joint under image-intensifier control while the lower limb is kept in 15° abduction, neutral rotation, and 0° flexion. This position is used so that the guidewire is perpendicular to the femoral shaft. The hinge of the monolateral articulated distraction device is aligned with this guidewire ( Fig. 1 ). Two half pins (5 or 6 mm) are inserted in the supra-acetabular area using the image intensifier for avoiding too-deep penetration. The author prefers the use of hydroxyapatite-coated pins. Another 2 or 3 pins are applied to the shaft of the femur in the midsagittal plane. The guide pin is removed and the range of motion of the hip is checked. A circular external fixator can be applied with the same principles as the monolateral hinged fixator. Schanz pins are introduced in a convergent manner into the iliac crest, the supra-acetabular area, or both, and fixed to a pelvic arch. Another arch or a complete ring is applied to the femur by wires or pins. The connection between the two parts is built using rods and hinges, ensuring that the level of the hinge is at the center of hip rotation as previously described. In cases with flexion hip deformity, an extension rod can be applied for a temporary period to correct the deformity and restrict all movements.
Postoperative protocol
Patients are allowed to walk with partial weight bearing with crutches on the second day after the operation. A day later, distraction is started at a rate of 1 mm/d. Distraction is continued until the Shenton line is overcorrected by 5 to 10 mm ( Fig. 2 ). Physiotherapy is performed daily to maintain hip flexion and extension. The end point of distraction is when adequate ossification of the lateral pillar is seen because no further collapse of the epiphysis is expected beyond this stage of the disease. This result would normally take 4 or 5 months in the fixator. After fixator removal, the child has daily hydrotherapy and physiotherapy with passive continuous and active assisted movements. Non–weight-bearing activity is recommended for 2 months.
