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Biomedical subjects

W C Head

Publications and source records attributed to W C Head.

At least 37 records · Page 2Linked to original sources
PubMed1995

Dealing with the deficient acetabulum in revision hip arthroplasty.

Variable bone loss is the defining feature of the failed acetabulum. Preoperative planning must include an assessment of the extent of bone deficiency. When bone loss precludes a routine revision there are three reconstructive options, a small cup in the false acetabulum, reconstruction of the lost bone with an allograft, and a jumbo cup filling the expanded acetabulum. The investigators have found that the latter technique can often be used in the setting of the difficult acetabulum with improvement in hip mechanics and avoiding a structural bone graft. When a graft is necessary, the best technique is a small graft and large fixed cup, with support of both the cup and graft on as much host bone as possible. A posterior buttressing plate should be considered for any graft providing substantial posterior support of the acetabular component.

Acetabulum↗
PubMed1995

Titanium as the material of choice for cementless femoral components in total hip arthroplasty.

Modern total hip arthroplasty has been performed using femoral stems manufactured from stainless steel, cobalt-chrome molybdenum alloy (CoCrMb), titanium aluminum vanadium alloy (TiAlV), and, on a limited basis, low-elastic modulus composites. Today, only CoCrMb and TiAlV are used in significant numbers. There is ample theoretical, experimental, and clinical evidence to support Ti-AlV as the material of choice for cementless femoral stems, based on superior mechanical compatibility and biocompatibility. The primary advantage of TiAlV over CoCrMb is a lower modulus of elasticity. This results in decreased stress shielding and subsequent favorable femoral remodeling. This effect is more significant with the smaller stem sizes used in primary surgery but persists even with larger stem sizes used in revision surgery. The second advantage of TiAlV is its biocompatibility. Titanium aluminum vanadium alloy is of relatively low toxicity in concentrations found clinically, and TiAlV is inert in the physiologic environment. With regard to fixation in cementless total hip arthroplasty, TiAlV has been shown to achieve excellent bone ingrowth into porous surfaces. In addition, there is evidence of superior bony ingrowth into TiAlV as compared with CoCrMb. Titanium aluminum vanadium alloy is presently the material of choice to be used in conjunction with hydroxyapatite coating. Prosthetic design, stem diameter, and porous-coating applications play significant roles in bony response regardless of metal composition.

Biocompatible Materials↗
PubMed1994

Revision total hip arthroplasty in the deficient femur with a proximal load-bearing prosthesis.

The proximal femur is frequently structurally deficient in revision hip arthroplasty, and makes obtaining prosthesis stability more difficult. Between 1984 and 1990, 174 patients were treated with revision total hip arthroplasty, performed by a standardized surgical technique, using cortical onlay strut allografts to restore the structural integrity of the femur, and a calcar replacement proximally porous-coated femoral prosthesis, composed of titanium alloy. The grafts united 98% of the time, and showed evidence of revascularization, and in some cases, complete incorporation. To date, six have been revised for femoral failure. Successful reconstruction of the deficient femur after failed total hip arthroplasty is dependent on several factors: the revision prosthesis must be stable, the deficient femoral bone stock must be augmented, and load must be transferred to the proximal femur so that the future proximal femoral resorption is minimized. The host femur and allograft will respond physiologically to load bearing, and the graft increases bone quantity and quality. The prosthesis must be supported primarily on host bone; the graft may enhance prosthetic support, but can never be used for primary prosthetic support when using uncemented revision prostheses.

Aged↗
PubMed1994

Extensor mechanism reconstruction with an allograft after total knee arthroplasty.

The authors report on a series of 15 knees in which an extensor mechanism allograft was used to treat a rupture of the patellar tendon associated with a total knee arthroplasty. Nine of the knees have greater than two-year follow-up evaluation (average, 4.1 years; range, 2.3-7 years). Postoperatively, the average flexion was 106 degrees. All but three patients achieved full passive extension. Six of the nine knees had no extensor lag. The average post-operative clinical score for the follow-up group was 78 points. Graft complications include one early graft rupture, one early quadriceps junction failure, and one patellar component loosening. One graft fractured after revision of a metal-backed patella.

Adult↗
PubMed1993

Dealing with the deficient acetabulum in revision hip arthroplasty: the importance of implant migration and use of the jumbo cup.

The complexity of acetabular anatomy makes operative planning for revision difficult. Plain radiographs do not provide as much detail about structural damage to the acetabulum as the surgeon would like in order to decide on the need for special components and bone grafts. The authors have found that analysis of acetabular implant migration has been a reliable surgical planning technique to indirectly assess residual acetabular bone stock. Superior shift on the anterioposterior radiograph implies posterior superior acetabular roof loss, seriously compromising the major weight-bearing area of the acetabulum. Although this may require a structural allograft, the authors have found that bone stock at the level of the true acetabulum is much better than in the false acetabulum created by the migration. Therefore, rather than a small cup placed high on the ilium, a large jumbo cup can frequently restore better hip biomechanics and take advantage of all of the remaining host bone for component stability and support, without the need for structural grafts. Medial shift implies medial superior migration leaving the physiologically strong rim of the acetabulum intact and therefore, less structurally damaging than posterior superior migration. Because the acetabular rim is anatomically designed for load bearing, a rim fit cup restores physiological weight transfer across the pelvis. Bone graft behind such a cup is protected from full weight-bearing forces and has proven to be very reliable.

Acetabulum↗
PubMed1993

Cortical strut allografts for femoral reconstruction in revision hip arthroplasty.

One hundred thirty-six cortical strut allografts fixed to the femur in revision hip surgery were studied using quantitative and qualitative radiographic analysis. In addition, 58 patients were clinically evaluated. The grafts showed a consistent behavior characterized by some resorption, bony bridging between host and graft, and a high incidence of union. The grafts showed evidence of revascularization and in some cases complete incorporation. The average Harris scores in the clinical group increased from 48 to 79 and was not influenced by the quality of bone before revision. Strut allografting of the femur in revision surgery is a reliable method of augmenting bone stock.

Adult↗
PubMed1993

Proximal femoral allografts in revision total hip arthroplasty.

The senior authors have performed 141 proximal femoral whole-bone allografts in failed total hip reconstruction. The results of the first 50 have been previously reported. This study reviews 70 additional cases performed since 1987 and reflects improved technique and several different junctional constructs. Modest improvements in the rate of union (64% v 80%) and of dislocation (28% v 16%) have been achieved. The infection rate (6% v 4%) and demographics of the groups have remained constant. The frequency of complications (67% v 53%) has decreased, but unfortunately remains high. A step-out allograft junction with a long lateral sleeve has been the most reliable construct.

Adult↗
PubMed1993

Restoration of femoral bone stock in revision total hip arthroplasty.

The presence of femoral deficiencies in revision total hip arthroplasty may contribute to loosening, subsidence, and fracture. Between 1984 and 1990, 174 patients were treated with revision total hip arthroplasty, preformed by a standardized operative technique using cortical onlay strut allografts to restore the structural integrity of the femur and a calcar deficient proximally porous coated femoral prosthesis, composed of titanium alloy. The grafts united 98% of the time and showed evidence of revascularization and, in some cases, complete incorporation. Cortical onlay strut grafting in conjunction with a proximal load- bearing prosthesis is a viable method of reconstructing the structurally deficient femur in revision total hip arthroplasty.

Aged↗
PubMed1992

Disease and specific considerations in total hip replacements.

Total hip replacement arthroplasty has evolved where multiple options may be provided to the patient depending on disease, age, activity level, bone quality, and bone geometry. For elderly patients, the hybrid hip (uncemented acetabular and cemented femoral components) is widely used. In the young active population, uncemented porous bone ingrowth designs predominate. Special considerations involving the total hip patient include management of blood loss anemia, prevention of infection, and prevention of heterotopic ossification. Autologous blood donation as well as collection and infusion of shed blood in the postoperative patient greatly minimize the need for homologous transfusions. Optimizing the surgical environment, meticulous and efficient surgical technique, and antibiotic prophylaxis continue to be the cornerstones of infection prevention. Nonsteroidal anti-inflammatory medication and radiation are effective means of preventing heterotopic ossification.

Adolescent↗
PubMed1992

Soft-tissue balance and alignment in medial unicompartmental knee arthroplasty.

We reviewed two similar groups of patients with medial osteoarthritis of the knee treated by unicompartmental arthroplasty. The group receiving an Oxford meniscal-bearing implant, with no medial release, showed significantly better mechanical alignment than that receiving a fixed-bearing implant. Under-correction, with its ominous mechanical implications, was much more common with the fixed-bearing design. Over-correction was rare and was seen in both designs about equally. Degenerative stenosis of the intercondylar notch was common and appeared to put the anterior cruciate ligament at risk of rupture, especially after correction of the varus deformity. We consider that postoperative leg alignment and soft-tissue balance after unicompartmental knee replacement are determined more by the implant design and the surgical technique than by any variation in soft-tissue contracture. Release of the medial collateral ligament is not necessary for realignment, but a generous notchplasty is often needed to allow normal anterior cruciate ligament function.

Follow-Up Studies↗
PubMed1992

Cortical strut allografts in the reconstruction of the femur in revision total hip arthroplasty. A basic science and clinical study.

Repeated total hip arthroplasties cause a loss of bone stock that will produce diminished component support, and can compromise implant function. There is, therefore, a compelling argument to return bone stock to the femur at the time of revision arthroplasty. Cortical strut allografts serve this purpose. They unite consistently and reliably, by 8.4 months on average. The overall rate of strut union is 96.6%. The sequence of healing events starts with round-off, followed by partial bridging and complete bridging. The repair process includes remodeling of the host femur, as well as the graft. Although there is variable resorption of some grafts, usually where not opposed to the host bone, there is also extension of others from host callus build-up such that, on average, there is no significant measurable loss of graft length or width. Most of the allograft struts, 78%, maintained a radiodense appearance. Clinical results of femoral revision with strut allografting have shown satisfactory end results compared with historic controls, with an average Harris score of 79.6 and a 2.7% subsidence rate. Of particular note is that the subsidence rate and clinical scores did not vary with the state of the preoperative femur, as has been shown repeatedly in the past. The canine model shows that the strut allografts are biologically active. Through mobilization of mesenchymal tissue, they are transformed into vascularized calluslike structures while maintaining good strength, and then further remodel to lamellar bone.

Animals↗
PubMed1992

Results of implant retrieval from postmortem specimens in patients with well-functioning, long-term total hip replacement.

The evaluation of postmortem specimens provides a unique opportunity to gain understanding of the interface between host and well-functioning prostheses unavailable from revision specimens that, by nature, are accompanied by the artifacts generated during their removal. The preliminary findings from the relatively limited number of specimens described in this collaborative study demonstrate the value of the effort and are presented to encourage surgeons to participate in this program and to make their patients aware of the value of the information they may provide.

Adult↗
PubMed1991

Prophylactic and early therapeutic use of the Greenfield filter in hip and knee joint arthroplasty.

The orthopaedic literature does not provide clear guidelines for the protection of the extremely high-risk thromboembolic patient undergoing hip and knee total joint or related reconstructive surgery. Nor is there agreement of how to protect the immediate postoperative patient with thromboembolic complications. The authors, believing that routine anticoagulation measures are ill-advised in these two circumstances, elected instead to place a Greenfield vena cava filter for prevention of life-threatening thromboembolism. Using prospective selection criteria, 47 patients could be followed over a 24-76-month period. There were no clinical embolic episodes in either group and no late complications of the filter placement. The few complications in this series were related to insertion, only one of which lead to minor long-term disability. The caval patency rate was 96%. The authors have concluded that such prophylactic use of the Greenfield vena cava filter is justified since it contributes to safer and more reliable total hip and total knee surgery with only minor morbidity.

Aged↗