Projected increase in total knee arthroplasty in the United States - an alternative projection model.

OBJECTIVE: The purpose of our study was to estimate the future incidence rate (IR) and volume of primary total knee arthroplasty (TKA) in the United States from 2015 to 2050 using a conservative projection model that assumes a maximum IR of procedures. Furthermore, our study compared these projections to a model assuming exponential growth, as done in previous studies, for illustrative purposes. METHODS: A population based epidemiological study was conducted using data from US National Inpatient Sample (NIS) and Census Bureau. Primary TKA procedures performed between 1993 and 2012 were identified. The IR, 95% confidence intervals (CI), or prediction intervals (PI) of TKA per 100,000 US citizens over the age of 40 years were calculated. The estimated IR was used as the outcome of a regression modelling with a logistic regression (i.e., conservative model) and Poisson regression equation (i.e., exponential growth model). RESULTS: Logistic regression modelling suggests the IR of TKA is expected to increase 69% by 2050 compared to 2012, from 429 (95%CI 374-453) procedures/100,000 in 2012 to 725 (95%PI 121-1041) in 2050. This translates into a 143% projected increase in TKA volume. Using the Poisson model, the IR in 2050 was projected to increase 565%, to 2854 (95%CI 2278-4004) procedures/100,000 IR, which is an 855% projected increase in volume compared to 2012. CONCLUSIONS: Even after using a conservative projection approach, the number of TKAs in the US, which already has the highest IR of knee arthroplasty in the world, is expected to increase 143% by 2050.

Increased risk of revision for high flexion total knee replacement with thicker tibial liners.

The outcome of total knee replacement (TKR) using components designed to increase the range of flexion is not fully understood. The short- to mid-term risk of aseptic revision in high flexion TKR was evaluated. The endpoint of the study was aseptic revision and the following variables were investigated: implant design (high flexion vs non-high flexion), the thickness of the tibial insert (≤ 14 mm vs > 14 mm), cruciate ligament (posterior stabilised (PS) vs cruciate retaining), mobility (fixed vs rotating), and the manufacturer (Zimmer, Smith & Nephew and DePuy). Covariates included patient, implant, surgeon and hospital factors. Marginal Cox proportional hazard models were used. In a cohort of 64 000 TKRs, high flexion components were used in 8035 (12.5%). The high flexion knees with tibial liners of thickness > 14 mm had a density of revision of 1.45/100 years of observation, compared with 0.37/100 in non-high flexion TKR with liners ≤ 14 mm thick. Relative to a standard fixed PS TKR, the NexGen (Zimmer, Warsaw, Indiana) Gender Specific Female high flexion fixed PS TKR had an increased risk of revision (hazard ratio (HR) 2.27 (95% confidence interval (CI) 1.48 to 3.50)), an effect that was magnified when a thicker tibial insert was used (HR 8.10 (95% CI 4.41 to 14.89)). Surgeons should be cautious when choosing high flexion TKRs, particularly when thicker tibial liners might be required.

Risk factors associated with surgical site infection in 30,491 primary total hip replacements.

We examined patient and surgical factors associated with deep surgical site infection (SSI) following total hip replacement (THR) in a large integrated healthcare system. A retrospective review of a cohort of primary THRs performed between 2001 and 2009 was conducted. Patient characteristics, surgical details, surgeon and hospital volumes, and SSIs were identified using the Kaiser Permanente Total Joint Replacement Registry (TJRR). Proportional-hazard regression models were used to assess risk factors for SSI. The study cohort consisted of 30,491 THRs, of which 17,474 (57%) were performed on women. The mean age of the patients in the whole series was 65.5 years (13 to 97; SD 11.8) and the mean body mass index was 29.3 kg/m(2) (15 to 67; SD 5.9). The incidence of SSI was 0.51% (155 of 30,491). Patient factors associated with SSI included female gender, obesity, and American Society of Anesthesiologists (ASA) score ≥ 3. Age, diagnosis, diabetes and race were not associated with SSI. The only surgical factor associated with SSI was a bilateral procedure. Surgeon and hospital volumes, use of antibiotic-laden cement, fixation method, laminar flow, body exhaust suits, surgical approach and fellowship training were not associated with risk of SSI. A comprehensive infection surveillance system, combined with a TJRR, identified patient and surgical factors associated with SSI. Obesity and chronic medical conditions should be addressed prior to THR. The finding of increased SSI risk with bilateral THR requires further investigation.

Localization of hyaluronan in pseudocapsule from total hip arthroplasty.

Hyaluronan is a large glycosaminoglycan present in normal synovial fluid imparting important viscoelastic properties for joint lubrication. In normal and noninflammatory conditions, hyaluronan has been localized to the lining layer of the synovial membrane, specifically synovial fibroblasts. Prosthetic joint fluid contains large amounts of hyaluronan, the source of which has not been determined. Pseudocapsules from patients who had total hip arthroplasty and were having revision surgery for nonloosened and nonseptic conditions were fixed in 10% acid formalin with 70% alcohol and stained for hyaluronic acid with biotinylated hyaluronic acid binding protein as a probe. Hyaluronan was localized strongly to the lining layer of the pseudocapsule, as in normal and osteoarthritic synovial membranes. The fibroblasts in the pseudocapsule of total hip arthroplasty may be responsible for the persistent production of hyaluronan in prosthetic joint fluid.

Cementless implant composition and femoral stress. A finite element analysis.

Proximal atrophy and thigh pain are recognized problems with some cementless femoral stems in total hip arthroplasty. It is thought that reduced femoral stress from alterations in load transfer caused by an intramedullary stem contributes to proximal femoral atrophy. An increase in flexural rigidity and bone stress near the stem tip is thought to contribute to thigh pain. A three-dimensional finite element analysis study was performed to calculate stresses in the proximal femur and bone near the stem tip before and after implantation of a collared, proximally coated, cementless femoral prosthesis. The influence of prosthetic material was examined by changing implant composition from cobalt chrome to titanium alloy and leaving all other parameters constant. Femoral stress was increased twofold immediately below the collar with the titanium implant compared with the cobalt chrome. However, the proximal femoral stress in the titanium implanted model was still 1/10 that in the corresponding region of the unimplanted femur model. At the stem tip, as much as a 30% reduction in femoral stress was seen with the titanium stem compared with the cobalt chrome. These findings suggest biomechanical evidence of an advantage for titanium as an implant material compared with cobalt chrome for cementless femoral stems.

Spontaneous repair of superficial defects in articular cartilage in a fetal lamb model.

A fetal lamb model was developed to investigate the capacity of fetal articular cartilage for repair after the creation of a superficial defect. Superficial defects, 100 micrometers deep, were made in the articular cartilage of the trochlear groove in the distal aspect of the femur in eighteen fetal lambs that were halfway through the 145-day gestational period; the contralateral limb was used as a sham control. The wounds were allowed to heal in utero for three, seven, fourteen, twenty-one, or twenty-eight days. Seven days after the injury, the defects were filled with a hypocellular matrix, which stained lightly with safranin O. At twenty-eight days, the staining of the matrix was similar to that of the sham controls and the chondrocyte density and the architectural arrangement of the cell layers had been restored. An inflammatory response was not elicited, and no fibrous scar tissue was observed.

Revision total hip arthroplasty with correctional femoral osteotomy in Paget's disease.

Varus alignment of the femoral component is associated with femoral component loosening in total hip arthroplasty performed for Paget's disease. Irregular and hemorrhagic bone, along with angular femoral deformity, was encountered during revision total hip arthroplasty in three pagetic patients. A diaphyseal femoral osteotomy facilitated cement removal and provided an opportunity for correction of the deformity. The step-cut configuration of the osteotomy provided intrinsic rotational stability of the femoral segments around a modular, long-stem cementless implant. Excellent clinical and radiographic results were achieved, but moderate blood loss and delayed healing of the osteotomy site were observed.

Tissue expansion for staged reimplantation of infected total knee arthroplasty.

Resection arthroplasty of a chronically infected total knee arthroplasty resulted in thin and contracted anterior skin. Expansion of skin using Silastic reservoirs (McGhan Medical, Santa Barbara, CA) facilitated wound closure and rehabilitation following staged total knee reimplantation. Prophylactic expansion of skin around the knee avoided salvage soft tissue procedures such as local and distant tissue flaps.

Posterior capsulorrhaphy in total shoulder arthroplasty. A case report.

The management of intraoperative posterior instability during total shoulder arthroplasty includes soft tissue balancing, reduction of humeral component retroversion, and augmentation of posterior glenoid defects. Severe instability caused by incompetence of the posterior capsule may require plication of the capsular remnant or a posterior muscle to the glenoid or proximal humerus. A technique of posterior capsulorrhaphy to the proximal humerus is described that does not require a separate surgical approach. By restoring stability, early range of motion exercises can be instituted, eliminating the need for postoperative immobilization. Posterior stability should be assessed during all total shoulder arthroplasties.

Bipolar revisions with bone-grafting for cavitary and segmental acetabular defects. A minimum 5-year follow-up study.

Bipolar revisions used in massive uncontained acetabular defects often lead to high migration rates and early clinical failure. Reconstructions for less severe acetabular bone deficiencies were studied radiographically and clinically. Thirty-two bipolar revisions with bone-grafting were performed for cavitary and segmental acetabular defects. The average follow-up period was 6 years (range, 5-8.4 years). Medial migration averaged 2.3 mm (range, 0-7 mm), oblique migration averaged 2.9 mm (range, 0-8 mm), and superior migration averaged 5.9 mm (range, 0-15 mm). Continued migration at the final follow-up evaluation was noted in all but nine hips. Arrested migration was observed when cavitary defects were encountered. Segmental medial wall defects resulted in increased medial migration. Segmental superior rim defects resulted in large amounts of superior migration. Preoperative Harris hip scores averaged 47 before surgery and 86 at the final follow-up evaluation. Postoperative clinical scores did not deteriorate with radiographic evidence of progressive migration. Six reoperations for femoral complications of fracture or loosening were performed at an average of 4.7 years with concomitant conversion of the bipolar prosthesis to a fixed cementless cup. One re-revision was performed for acetabular disassembly at 6.6 years. When cavitary defects exist, allografting with a bipolar endoprosthesis can provide durable reconstructions with excellent clinical function. Bipolar revisions are also a relatively simple means of providing stability in recurrent dislocation cases.

151 endoprosthetic reconstructions for patients with primary tumors involving bone.

As part of the UCLA limb salvage program, 151 patients received 151 endoprostheses for primary tumors involving bone. Follow-up of all patients was to death (56), revision (21), or a minimum two years for the 74 additional survivors (range: 24-114 months; mean: 52 months). Endoprosthetic replacements were of the distal femur (81), proximal femur (19), proximal humerus (13), proximal tibia (11), scapula (11), total femur (8), total humerus (4), intercalary prostheses (2), and one each of the distal humerus and the pelvis. There were three soft tissue sarcomas, five benign bone lesions, and 143 primary malignant tumors of bone. MSTS function was good-excellent in 78%. There were 64 local complications in 55 patients (36%). Mechanical failure occurred in 24 patients (15.9%), local recurrence occurred in ten (6.6%), minor wound healing problems in nine (5.9%), and infection in eight (5.3%). Few systemic complications were reported. Function appeared to be location dependent. All of the 29 patients with benign or low grade malignant tumors (parosteal, IA, IB) have survived. Of the 116 patients with stage IIA and IIB disease, 59% survived three years, and a Kaplan-Meier analysis projects that 56% are expected to survive at five years. Only 17 (11%) of these 151 endoprostheses have been revised; an additional four (3%) eventually came to amputation. The Kaplan-Meier analysis revealed that 91% of the prostheses survived three years and 83% survived five years. The Cox Proportional Hazards model revealed that for patients with stage IIA and IIB disease, the risk of death is four times the risk of the need for revision at five years. Although endoprosthetic reconstructions have their own unique complications, they have proven durable in this series of patients. Local problems usually can be managed without amputation, and patient satisfaction is high.

Intra-articular corticosteroid reduces joint stiffness after an experimental periarticular fracture.

Early care after surgery or trauma to the extremities often includes a period of immobilization. The resultant joint stiffness may require extensive rehabilitation and may permanently limit function of the limb. Posttraumatic joint stiffness is particularly vexing in the small joints. In an experimental model, we tested the effects of intra-articular corticosteroid injections on stiffness in a joint at risk of posttraumatic joint stiffness. Triamcinolone was injected into ankle joints of rabbits after distal tibial fractures. Three weeks after injury, joint stiffness increased 34% in ankles injected with the steroid. Stiffness in ankles injected with saline solution and in ankles treated with no injection increased 133% and 224%, respectively. Limb swelling and tibial torsional strength to failure were not significantly affected by either of the treatments.

Continuous passive motion versus immobilization. The effect on posttraumatic joint stiffness.

Management of intraarticular fractures is often complicated by joint stiffness long after bony healing has occurred. The following experiments provide biomechanical evidence for the effectiveness of CPM in maintaining joint function in stabilized articular injuries. The ankles of ten adolescent New Zealand white rabbits were penetrated by Steinmann pins to create an intraarticular injury. One limb of each animal was immobilized, and the contralateral limb was placed in a continuous passive motion (CPM) machine for three weeks. Joint stiffness of each ankle was quantified with an arthrograph before injury and after three weeks of treatment. Hindlimb volumes were recorded before injury and monitored at weekly intervals using a water-displacement method. Joint stiffness increased 2.6 times the preinjury levels in limbs that were immobilized for three weeks. There was no statistically significant increase in joint stiffness in ankles treated with CPM compared to preinjury values. The posttraumatic difference between the CPM-treated and immobilized limbs was highly significant; limb swelling was not affected by CPM.

Total hip replacement for patients who have ankylosing spondylitis. The importance of the formation of heterotopic bone and of the durability of fixation of cemented components.

Fifty-three total hip replacements were performed in thirty-one patients who had ankylosing spondylitis. After an average period of follow-up of 6.3 years, cemented conventional hip prostheses proved to be very durable in this young population (average age, forty-three years). Only one primary conventional hip prosthesis was revised for aseptic loosening, seventeen years after implantation. Clinically important heterotopic bone (Classes III and IV of Brooker et al.) developed in 11 per cent of the patients, all of whom had had a previous operation on the hip, postoperative infection, or complete ankylosis preoperatively. If a patient has clinically important heterotopic bone after one operation on the hip, and an arthroplasty of the contralateral hip or reoperation on the same hip is to be done, prophylactic treatment should be considered for prevention of formation of heterotopic bone.

Biomechanical effects of point configuration in Kirschner-wire fixation.

The drilling and bone holding properties of Kirschner wires of three different tip designs have been investigated. The tip designs studied were the commercially available trocar- and diamond-shaped tips and the homemade cut tip produced by cutting the pin obliquely with wire cutters. Thirteen canine metacarpals were drilled with wires of each tip design at 400 and 800 rpm. A servohydraulic test machine (Materials Test Systems, Minneapolis, MN) simultaneously measured axial loads, torque, and displacement during insertion and pull-out. Kirschner wires of each tip configuration were also placed in seven canine metacarpals for a three-week in vivo test. After the animals were killed, peak pull-out forces were measured and compared with in vitro results. The trochar-tipped wire displayed the highest required torque and axial load to penetrate bone. It also demonstrated the highest pull-out force immediately after drilling, especially when inserted at the low drill speed. After placement for three weeks, pull-out force of the diamond-tipped wire equaled the trochar. The homemade cut wire consistently yielded inferior holding properties. For immediate and sustained strong fixation in bone, a wire with a trochar tip configuration should be inserted at low drill speeds.