Metabolic Bone Diseases and Total Hip Arthroplasty: Preventing Complications

Joaquin Moya-Angeler, MD, PhD; Joseph M. Lane, MD; Jose A. Rodriguez, MD

Disclosures

J Am Acad Orthop Surg. 2017;25(11):725-735. 

In This Article

Acetabular and Femoral Concerns

Acetabular Defects

Most acetabular defects encountered in primary THA are the result of protrusio acetabuli, developmental dysplasia of the hip, and trauma.[30] Protrusio acetabuli results from primary (idiopathic) or secondary factors, such as infectious, neoplastic, inflammatory, metabolic, traumatic, or genetic causes.[31] Although the prevalence of this condition has not yet been determined, some authors think that many patients diagnosed with primary protrusio acetabuli have metabolic abnormalities that were overlooked.[31] Osteomalacia and Paget disease have been identified as etiologic factors with an incidence as high as 50%.[11,31] Other MBDs that can result in protrusio acetabuli are osteogenesis imperfecta, SCD, ochronosis, acrodysostosis, and hyperparathyroidism[10,11,31] (Figure 4, A; Table 1).

The primary concerns related to protrusio acetabuli include both mechanical and biologic issues (Table 2). The objectives of THA in a patient with protrusio acetabuli depend on the degree of deformity and may include reinforcement of the medial wall, restoration of the acetabular integrity, lateralization of the acetabular implant, and rigid fixation with appropriate coverage of the defect.[30,32,33] The femoral side should always be considered to select an adequate level of femoral neck resection to optimize the center of rotation and limb length. During the surgical procedure, the surgeon may have trouble exposing the femoral neck and dislocating the hip. An in situ femoral neck cut with subsequent removal of the femoral head can be useful in those instances. Alternatively, a portion of the overhanging acetabular wall or ossified labrum can be removed to allow extraction of the femoral head. One key element when preparing the acetabulum is to ream carefully, avoiding penetration of the medial wall. It is therefore crucial not to deepen the socket and ream peripherally to achieve good rim contact.

Several techniques can be used to restore the center of rotation of the hip. These techniques include cement augmentation, the use of different types of bone grafts or augments, and/or the use of supporting cups.[30,32] In very elderly patients, an acetabular cup can be cemented on top of a large cement mantle in combination with a wire mesh. However, the reported results of this method are conflicting and suggest additional concerns of thermal osteolysis of the medial wall and early loosening.[30] The optimal method of cup lateralization is the use of bone graft, which can be used to build up the defect to allow the use of cemented or noncemented acetabular implants. Currently, the most widely used approach is to fill the defect with morcellized graft and then use a porous-coated metal cup to reconstruct the acetabulum.[30,32] The noncemented porous socket requires rigid fixation and contact with viable host bone. Cemented cups are a useful option in patients with severely osteoporotic bone, with immediate gratifying results; however, late lucencies appear and lead to loosening.[30] Occasionally, antiprotrusio cages may be required for a primary reconstruction, although they are intended to be used in the revision setting in the absence of native bone stock.[30]

Proximal Femoral Abnormalities

Proximal femoral abnormalities that can complicate THA have been reported in conjunction with some MBDs. These conditions include Paget disease (coxa vara); diseases associated with large femoral canals, such as ankylosing spondylitis; and diseases associated with narrow femoral canals, such as achondroplastic dwarfism, spondyloepiphyseal dysplasia, and SCD.[5,10,24,26] The shepherd crook deformity, a specific proximal femoral deformity characterized by a severe varus deformity with a reduction in the neck shaft angle >90°, is associated with fibrous dysplasia, Paget disease, osteogenesis imperfecta, and other MBDs.[10,11,27,28]

Femoral deformities can be classified on the basis of the location and geometry of the deformity[34] (Table 3). These factors should determine the type of implant to use, its size and position, and the need for a corrective femoral osteotomy.[35] Deformities at the level of the greater trochanter may compromise access to the femoral canal (overhanging trochanter) or result in extra-articular impingement with the pelvis and a decreased lever arm of abduction (high-riding greater trochanter). In patients with these deformities, a trochanteric osteotomy with advancement repositioning can be done to allow access for implant fixation and reduce the likelihood of inadvertent trochanteric injury.[31,32] Abnormalities at the level of the femoral neck (varus/valgus) may affect the abductor lever arm of the hip and leg length. Varus femoral necks may require the use of lateral offset stems to address those issues, whereas valgus femoral necks may require normal or modified implants (with reduced metaphyseal flare).[36] In patients with excessive varus that cannot be reproduced with high-offset implants, lengthening of the leg may be necessary to have sufficient soft-tissue tension to prevent dislocation.[36]

Torsional abnormalities can cause an inappropriate range of motion and hip instability when the femoral implant is positioned according to the native version.[31] If the appropriate version cannot be achieved with a regular femoral implant, alternatives that can be considered include cemented femoral implants, modular stems with proximal fixation, tapered stems (monoblock or modular) for distal fixation, customized implants, and/or derotational femoral osteotomies.[32,36] Those options should also be considered in patients with metaphyseal deformities that would compromise proximal fit with regular noncemented monoblock stems.[36] Angular or rotational deformities at the level of the diaphysis may require a corrective osteotomy if the deformity is not sufficiently distal to accommodate a short-stem implant or a cemented implant.

Another aspect that should be evaluated is the diameter of the femoral canal.[37] A thin or narrow canal may compromise the preparation of the femoral canal with standard instruments, whereas an excessively wide canal may affect bone ingrowth and/or cement interface.[37] The incidence of complications of THA in patients with proximal femoral deformity is high in most published series, with femoral perforation and fractures being the most common complications.[31,32] The use of intraoperative fluoroscopy during stem insertion can help to prevent fractures.

Bone Quality

Because most patients with MBDs have structurally abnormal bone, the assessment of the quality and quantity of bone is an essential part of the preoperative planning in patients with MBDs undergoing hip arthroplasty.[1,5,37,38] The presence of sclerotic bone in the acetabulum can make reaming challenging and can cause difficulties in placing the acetabular component in the correct location. In patients with notably sclerotic bone, uniform reaming can be challenging to achieve.[16] Distinct changes in the quality of the bone may be encountered during reaming, such that when the sclerotic bone is encountered superiorly, the reamer can be pushed into the softer medial bone, which can result in excessive medial reaming. However, during acetabular reaming in patients with osteoporotic bone, the reamers should be used at lower speeds, and the surgeon should check the results of the reaming frequently to avoid penetration of the acetabulum.[12,16] In addition, in patients with osteoporosis, the amount of underreaming required to achieve press fit must be considered. Because osteoporotic bone is more brittle and vulnerable to fracture than nonosteoporotic bone, the surgeon should consider decreasing the mismatch between the size of the final reamer and the implant size to reduce the chance of fracture.[18] This consideration is especially important in patients treated with steroids.

On the femoral side, the presence of sclerotic bone may complicate the use of standard rasps and reamers. In these patients, the use of high-speed burrs or flexible canal reamers can help to prevent complications, such as fracture or canal perforation. The shape of the osteoporotic femur has been found to be different from that of the nonosteoporotic femur (as bone density decreases, the bone widens and has thinner cortices). Dorr et al[38] described a classification based on the shape of the osteoporotic femur (Figure 5). In general, a cemented femoral implant is a reliable option for use in patients with an osteoporotic femur.[12,16] In these patients, noncemented stems are associated with concerns of subsidence and fracture because the anatomically designed stem may not fit the shape of the osteoporotic femur.

Figure 5.

Images demonstrating the Dorr classification of femoral bone quality. A, Type A has a champagne-flute shape (wide cortices). B, Type B is widened on the AP plane. C, Type C is widened on both planes, resulting in a stovepipe shape. (Reproduced with permission from Dorr LD, Faugere MC, Macek AM, Gruen TA, Bognar B, Malluche HH: Structural and cellular assessment of bone quality of proximal femur. Bone 1993;14[3]:231–242.)

Comments

3090D553-9492-4563-8681-AD288FA52ACE

processing....