3.1 Lower extremity angular deformity should be surgically corrected if the deformity is progressive or severe as defined by interference with gait, or by the presence of a mechanical axis deviation of more than 10° between the femur and tibia. Control of secondary HPT is recommended prior to surgical correction. (OPINION)
3.2 Symptomatic proximal femoral slipped epiphyses (SCFE) should be surgically stabilized if KDOQI target values for PTH are not achieved within 3 months of the diagnosis of SCFE. (OPINION)
Renal osteodystrophy refers to the effects of chronic renal failure (CRF) on the skeletal system. Although the underlying defect is metabolic in nature, this section is primarily concerned with the consequences of CKD most likely to be encountered by the orthopedic surgeon. These issues are largely the result of mechanical failure superimposed on the underlying metabolic and histological changes. They occur either acutely as seen in pathological fractures, or on a chronic basis as exemplified by severe and progressive knock-knees and bow-legs. From an orthopedic perspective, skeletal abnormalities are primarily the result of 2° HPT. Along with optimal metabolic treatment of these patients is a need for concurrent orthopedic management.
General
Prompt treatment of musculoskeletal deformity prevents further deformity, restores patient function and mobility, and improves patient self-esteem. Patients with renal osteodystrophy exhibit delayed acquisition of motor milestones. Skeletal age is also delayed, and short stature is to be expected with children often falling below the 5th percentile in height.44 The role of the orthopedist is to recognize these associated conditions, refer for management of metabolic issues (including possible GH treatment), and treat bony deformity. One of the frequently overlooked associations is a severe myopathy. Resistance training in adults can result in significant increases in both muscle mass and strength, and physical therapy is an essential part of treatment for these patients.45
The treatment of musculoskeletal complications must be tailored to the individual. Medical stabilization of 2° HPT is an important component of the care of angular deformity and slipped epiphyses. When surgery is necessary, medical management to achieve metabolic stability is of great importance. This improves surgical fixation and healing by improving the biomechanical strength of bone while limiting the incidence of postoperative recurrence. Elevated serum alkaline phosphatase levels (above 500 U/L) are associated with poor healing and continued bony deformity despite surgery.46,47
Angular Deformities
Angular deformity of the weight-bearing bones is the most common musculoskeletal abnormality in children with renal osteodystrophy. Of these, the most common is genu valgum, although genu varum, ankle valgum or varum, and coxa vara may also be seen.48,49 The cause of angular deformity is likely multifactorial. Metabolic abnormalities suppress physeal maturation, and asymmetric forces placed across the physis may compound the situation according to the Heuter-Volkmann principle (excessive compressive forces inhibit physeal growth).50 Finally, slipping of the epiphyses (discussed below) with subsequent healing may also result in residual angulation.
Although no one parameter predicts which patients go on to angular deformity, there is general consensus that it is related to metabolic instability, and that prompt correction of this instability can lead to improvement of skeletal deformity.46, 51-55 The age at onset of renal failure impacts which deformity is more common. Patients with physiological knee varus at the onset of renal failure tend to develop genu varum, while older patients with physiological valgus at disease onset tend to develop genu valgum.48
Evaluation of patients with angular deformity56 can be quantified with clinical photographs.56 For deformity out of the range of normal, standing lower extremity radiographs from hips to ankles on a 36” cassette are warranted. Deformity may be primarily at the distal femur, or proximal tibia, or variably divided between them. Angular deformity can improve with medical therapy alone.51 Patients without much growth remaining or with severe deformity are unlikely to satisfactorily improve, and they are usually treated with corrective osteotomy.47, 49 Patients with open physes and moderate valgus deformity may be treated with medial hemiepiphyseal stapling.47
Surgery is indicated when correction of the metabolic bone disease does not lead to resolution. The goal of surgery is to restore a normal anatomic axis such that a straight line passes simultaneously through the femoral head, center of the knee, and center of the ankle (talar surface), with the patient in a standing position. In addition, the ankle and knee joints should be parallel to the floor. Depending on the relative contribution of the distal femur versus the proximal tibia, the condition may require osteotomies above, below, or simultaneously above and below the knee joint in order to achieve these goals. Occasionally a varus deformity in the distal tibia may require a separate correction at that level.
Slipped Epiphyses
In contrast to adolescent idiopathic slipped epiphyses, slipped epiphyses in the renal osteodystrophy patient commonly occur through the metaphyseal—and not the physeal—regions of long bones. Although the most typical location is the proximal femur, slips have been reported in the distal radius and ulna, distal femur, proximal humerus, and distal tibia and fibula.48, 57-60 They likely occur due to 2° HPT, which leads to osteopenia and fibrosis of the metaphysis, thereby weakening it. Application of shear forces through weight bearing or unequal muscle pull at the ends of long bones are presumably the forces leading to gradual deformity through the area.
With lower extremity slips, patients usually present with an abnormal waddling gait. Upper extremity slips usually result in obvious skeletal deformity, though subtle deformity can be overlooked because these patients have widening of the metaphyses of long bones, giving them a pre-existing abnormal appearance at any rate. Radiographs of the affected areas are diagnostic. The vast majority of slips stabilize with medical treatment of the bone disease.57,58,61 Biomechanically, slip progression with further varus deformity is likely and can be prevented by medical and surgical stabilization of the slip. Therefore, if medical stabilization is not achieved promptly, pinning is undertaken.57 Many children are less than 10 years when the hips first slip, and many children do not close their physes for another 10 years since maturation is delayed. Thus, terminally smooth pins are usually placed with threads engaging bone only at the lateral cortex of the femur. This allows continued growth of the physis along the axis of the smooth portion of the pin.62 For non-hip-slipped epiphyses, observation and medical therapy alone are indicated, as long as there is skeletal growth remaining and the deformity is improving. An unacceptable deformity in a patient with little or no skeletal growth remaining is treated with surgical stabilization.
Avascular Necrosis
Avascular necrosis of bone occurs in the setting of CRF. The femoral head is a common site, and symptoms are often mild when compared to the radiographic appearance.63 While GH treatment may play a role in the development of AVN in these patients,64 the majority of reports associate the incidence of AVN with chronic immunosuppression after renal transplantation.48, 65-67 The incidence of this complication appears to be dose-related, though no specific dose-time guidelines exist.65,68,69 While the femoral head is the most common site, reports delineate the talus, humeral head, femoral condyles, and metatarsals as other involved sites. The diagnosis can be somewhat confusing in these patients because approximately 20% develop osteosclerosis, the cause of which is poorly understood. The increased bone density seen radiographically with avascular necrosis before collapse can have a similar appearance to osteosclerosis. The advent of magnetic resonance imaging (MRI) has aided in making a more secure diagnosis.
Case-based series of children with either SCFE or lower-extremity angular deformities support the idea that prompt optimal metabolic control is an integral component of the orthopedic care. There are only retrospective studies regarding the surgical treatment of angular deformity and SCFE. 46,47,57,62
Because few centers treat large numbers of patients with renal osteodystrophy, no prospective studies exist regarding optimal treatment of the orthopedic manifestations of the disease. Treatment recommendations are therefore largely based on the opinions of those who treat the largest number of these patients.
Although it is accepted that metabolic disease control is important if surgery is planned, future studies should examine the importance of control duration in the perioperative period and how this relates to surgical outcome. Also, the musculoskeletal manifestations of disease can improve with metabolic disease control, and a prospective study examining deformity improvements without surgery might lead to a better understanding of surgical indications. Studies comparing different surgical techniques for treatment of angular deformity are needed, as are studies exploring the optimal surgical fixation for SCFE stabilization.