In light of recent regulatory initiatives, medical devices now require additional clinical evidence to prove their safety and efficacy. At the same time, patients' own assessment of their devices' function and performance has gained in importance. The collection of these data allows for a more comprehensive picture of clinical outcomes and complications following total knee arthroplasty (TKA).

These trends have led researchers to search for new methods of acquiring, interpreting and disseminating patient-reported outcome measurements (PROMs). The current study assesses the feasibility of a digital platform for collecting PROMs that was recently adapted for TKA patients. It sought to determine patient engagement, survey completion rates, and satisfaction with this platform.

Eighty-two patients (mean age, 63.7 years, 59% females) scheduled for TKA were enrolled from one US and six UK sites between January 12, 2018 and April 30, 2018. Patients were supplied with a mobile application (app) that collects a variety of PROMs, including four domains based on the Patient-Reported Outcome Information System (PROMIS™): physical function, depression, pain interference and pain behavior. The platform electronically administers questionnaires using computer-adaptive tests (CATs), which reduce the burden on patients by tailoring follow-up questions to account for their previous answers. Satisfaction with the app was assessed in subset of patients who evaluated its ease-of-use (n=45), likelihood that they would recommend it to family/friends (n=35), and whether they successfully used the information it provided during their recovery (n=31). These scores were taken on a 1 to 10 (worst to best) scale.

Patients demonstrated regular engagement with the platform, with 73% using the app at least once a week. Weekly engagement remained high throughout the seven-week post-operative period (Figure 1). There was a 69% completion rate of all PROMIS™ CAT surveys during the study. The four PROMIS™ CAT domains had similar survey completion rates (Figure 2). The subset of patients queried regarding their satisfaction with the app gave it favorable mean scores for ease-of-use (8.8), likelihood to recommend to a family member or friend (8.1), and their success at using its information to improve their recovery (7.4).

Initial results support this digital platform's potential for successfully and efficiently collecting large volumes of PROMs. Patients reported high levels of engagement and satisfaction.

For any figures or tables, please contact authors directly.

Instability after TKA can result from ligament imbalance, attenuation of soft tissues, or ligament disruption. Flexion instability has been reported after both CR and PS TKA. However, the clinical manifestations of flexion instability can be quite variable. Symptoms of flexion instability include pain and swelling after activity. Bracing occasionally can be helpful. Revision options to treat flexion instability include tibial insert exchange and revision to increase constraint. However, more favorable results have been reported using implants with varus-valgus constraint.

Constrained mechanisms include a varus-valgus constrained PS post or hinge. The constrained post relies on the mechanical function of the post to provide stability which may deform or wear in-vivo leading to recurrent instability if used for a completely deficient collateral ligament. The hinge, which provides more rigid constraint, is indicated for collateral ligament deficiency. However, the additional constraint also results in greater bone-implant interface stresses, which may be mitigated by use of stem fixation to minimise risk of loosening.

Most acetabular defects can be treated with a cementless acetabular cup and screw fixation. However, larger defects with segmental bone loss and discontinuity often require reconstruction with augments, a cup-cage, or triflange component – which is a custom-made implant that has iliac, ischial, and pubic flanges to fit the outer table of the pelvis. The iliac flange fits on the ilium extending above the acetabulum. The ischial and pubic flanges are smaller than the iliac flange and usually permit screw fixation into the ischium and pubis. The custom triflange is designed based on a pre-operative CT scan of the pelvis with metal artifact reduction, which is used to generate a three-dimensional image of the pelvis and triflange component. The design of the triflange involves both the manufacturing engineer and surgeon to determine the most appropriate overall implant shape, screw fixation pattern, and cup location and orientation.

A plastic model of the pelvis, and triflange implant can be made in addition to the triflange component to be implanted, in order to assist the surgeon during planning and placement of the final implant in the operating room. A wide surgical exposure is needed including identification of the sciatic nerve. Proximal dissection of the abductors above the sciatic notch to position the iliac flange can risk denervation of the abductor mechanism. Blood loss during this procedure can be excessive.

Implant survivorship of 88 to 100% at 53-month follow-up has been reported. However, in a series of 19 patients with Paprosky type 3 defects, only 65% were considered successful. The custom triflange also tends to lateralise the hip center which may adversely affect hip mechanics. The use of a triflange component is indicated in cases with massive bone loss or discontinuity in which other reconstructive options are not considered suitable.

Abductor deficiency after THA can result from proximal femoral bone loss, trochanteric avulsion, muscle destruction associated with infection, pseudotumor, ALTR to metal debris, or other causes. Constrained acetabular components are indicated to control instability after THA with deficient abductors. However, the added implant constraint also results in greater stresses at the modular liner-locking mechanism of the constrained component and bone-implant fixation interface, which can contribute to mechanical failure of the constrained implant or mechanical loosening.

Use of large heads has been effective in reducing the rate of dislocation after primary THA. However, relatively large (36mm) heads were not found to be effective in controlling dislocation in patients with abductor deficiency. Dual mobility implants which can provide considerably larger head diameters than 36mm may offer an advantage in improving stability in patients with abductor deficiency. However the utility of these devices in controlling instability after THA with deficient abductors has not been established.

Whiteside has described a transfer of the tensor muscle and anterior gluteus maximus to the greater trochanter for treatment of absent abductors after THA. Transposition of the tensor muscle requires raising an anterior soft tissue flap to the lever of the interval between the tensor muscle and sartorius, which is the same interval used in an anterior approach to the hip. The muscle is transected distally and transposed posteriorly to attach to the proximal femur. This can result in soft tissue redundancy between the posterior tensor muscle and anterior gluteus maximus. This interval is separated and the anterior gluteus maximus also attached to the proximal femur. The transposed tensor muscle provides muscle coverage over the greater trochanter, which may be beneficial in controlling lateral hip pain.

In our practice, 11 patients were treated with Whiteside's tensor muscle transfer. Six patients had absent abductors, one had an avulsed greater trochanter, and four intact but weak abductors. One patient had a muscle transposition alone, one had an ORIF of the greater trochanter and muscle transposition, two had a muscle transposition and head/liner exchange, three had a muscle transposition and cup revision, two had a femoral revision and liner exchange with muscle transposition, and two had a muscle transposition with both component revision. None of the patients had constrained components.

The mean pre-operative abductor strength was 2.2 (0/5 in four patients 3/5 in four patients, and 4/5 in three patients). Pre-operative lateral hip pain was none or mild in two patients, moderate in three, and severe in six patients. Mean post-operative abductor strength was 3.2 (2/5 in four patients, 3/5 in three, 4/5 in two, 5/5 in two patients). Post-operative lateral hip pain was none in five and mild in six patients. One patient sustained a dislocation four weeks after surgery which was treated with open reduction. All of the other hips have remained stable.

Treatment of patients with hip instability and abductor deficiency has generally required use of a constrained acetabular component. In our experience, transfer of the tensor muscle and anterior gluteus maximus to the greater trochanter can improve abductor strength by one grade and also reduce lateral hip pain. The combination of a large head and tensor muscle transposition may be a viable alternative to use of a fully constrained component in patients with deficient abductors after THA. However, the need for implant constraint should also be individualised and based on factors such as the viability of the transposed muscle, patient compliance with post-operative activity restrictions, femoral head/neck ratio, and cup position.

Limited motion is associated with functional impairment and lack of satisfaction after total knee arthroplasty (TKA). The development of limited motion after TKA is often multifactorial. Patient related factors that can contribute to limited motion include poor pre-operative motion, patella infera, hip flexion contracture, leg length inequality, habitual narcotic use, morbid obesity, and possible genetic factors which lead to a biologic predisposition to form scar tissue. Surgical techniques to achieve full motion include appropriate sizing and positioning of the implants, proper gap balancing and soft tissue release, removal of posterior condylar osteophytes, and adequate tibial slope. Patient education, pain management, and participation in post-operative rehabilitation are also important. If adequate motion is not achieved, then manipulation can be helpful particularly up to three months after surgery. Once scar tissue is more mature, 6 months to a year after surgery, arthroscopy to resect arthrofibrotic scar is an appropriate option. For stiffness beyond one year after surgery revision TKA can be expected to result in modest improvement in motion, but pain relief may be quite variable.

The Vancouver classification separates periprosthetic femur fractures after THA into three regions (A - trochanteric, B - around or just below the stem, and C - well below the stem), with fractures around or just below the stem further separated into those with a well-fixed (B1) or loose stem and good (B2) or poor (B3) bone stock. Trochanteric fractures may be associated with osteolysis and require treatment that addresses osteolysis as well as ORIF of displaced fractures. Fractures around a well-fixed stem can be treated with ORIF using cerclage or cable plating, while those around a loose stem require implant revision usually to a longer cementless tapered or distally porous coated cementless stem. Fractures around a loose stem with poor bone stock in which salvage of the proximal femur is not possible require replacement of the proximal femur with an allograft prosthetic composite or proximal femoral replacement. Fractures well below the stem can be treated with conventional plating methods.

Periprosthetic acetabular fractures are rare and usually occur in the early post-operative period or late as a result of osteolysis or trauma. These can generally be separated into those with a stable acetabular component which can be treated non-operatively, and those with an unstable component often with discontinuity or posterior column instability which require complex acetabular reconstruction utilizing plating or revision to a cup-cage.

Abductor deficiency after THA can result from proximal femoral bone loss, trochanteric avulsion, muscle destruction associated with infection, pseudotumor, ALTR to metal debris, or other causes. Whiteside has described a transfer of the tensor muscle and anterior gluteus maximus to the greater trochanter for treatment of absent abductors after THA. Transposition of the tensor muscle requires raising an anterior soft tissue flap to the lever of the interval between the tensor muscle and sartorius, which is the same interval used in an anterior approach to the hip. The muscle is transected distally and transposed posteriorly to attach to the proximal femur. This can result in soft tissue redundancy between the posterior tensor muscle and anterior gluteus maximus. This interval is separated and the anterior gluteus maximis also attached to the proximal femur.

Relatively large unconstrained (36 mm heads) were not found to be effective in controlling dislocation in patients with abductor deficiency. In our practice, 11 patients with abductor deficiency were treated with Whiteside's tensor muscle transfer and an unconstrained large diameter femoral head. The mean pre-operative abductor strength was 2.2 and improved to 3.2 post-operatively. One patient sustained a dislocation four weeks after surgery which was treated with open reduction. All of the other hips have remained stable. The combination of a large head and tensor muscle transposition may be a viable alternative to use of a fully constrained component in patients with deficient abductors after THA.

Acetabular protrusio is defined radiographically as migration of the femoral head medial to Kohler's line (a line from the lateral border of the obturator foramen to the medial border of the sciatic notch). Protrusio can develop in association with metabolic bone diseases such as osteogenesis imperfecta, Marfan's Syndrome, and Paget's disease, inflammatory arthritis or osteoarthritis, tumors, or result from prior trauma. Acetabular protrusio can cause limited hip motion due to impingement of the femoral neck against the acetabular rim. When protrusio develops in association with osteoarthritis, coxa vara is often also present.

Surgical treatment of acetabular protrusio during total hip arthroplasty should lateralise the center of the hip to its anatomic position. This typically can be achieved with use of a larger, slightly oversized, rim fit cementless acetabular component and medial morselised femoral head bone autograft. In cases with more severe deformity, a reconstruction cage may be required. Alternatively a medialised acetabular shell can be used with a lateralised liner. If coxa vara is also present, standard femoral component position (approximately 1cm above the lesser trochanter) can result in an increase in leg length. Careful pre-operative templating should be performed and may require more distal placement of the femoral component to avoid overlengthening the limb.

The process by which pathologic scar tissue forms after TKA and restricts functional range of motion is relatively poorly understood. Arthrofibrosis may develop in patients who have normal intra-operative range of motion (ROM). However, passive flexion, extension, or both can become restricted and painful, sometimes several weeks after surgery following an early post-operative period of normal motion. The response to both nonsurgical and surgical treatment is often unsatisfactory. Arthrofibrotic scar contains dense fibrous tissue with abundant fibroblasts. Heterotopic bone is frequently found in patients with arthrofibrosis.

Stiffness may result from inadequate postsurgical pain management or rehabilitation or from a biologic process that causes rapid proliferation of scar tissue. Genetic factors also may play a role, although it is difficult to predict which patients are at increased risk for arthrofibrosis after TKA. Surgical technique also can contribute; oversizing the femoral component, overstuffing the patella, or rotational malalignment can play a role.

Manipulation can be helpful, particularly during the first three months after surgery. However, maintaining motion long term also requires an effective pain management and physical therapy program after manipulation. Arthroscopy may also have a role to remove scar tissue in the suprapatellar pouch and medial and lateral gutters usually between six months and one year after TKA. After one year following TKA, open surgical release or revision surgery is the most effective method to increase motion. However, only modest gains are likely to be achieved and pain may not be improved.

Introduction:

Acetabular revision Jumbo cups are used in revision hip surgeries to allow for large bone to implant contact and stability. However, jumbo cups may also result in hip center elevation and instability. They may also protrude through anterior wall leading to ilopsoas tendinitis.

The purpose of the current study was to compare mid-term outcomes of posterior cruciate retaining(CR) versus posterior cruciate substituting (PS)procedures, using the Genesis II total knee arthroplasty (TKA) system(Smith and Nephew, Memphis TN). Ninety nine CR and 93 PS TKA’s were analysed in this prospective, randomised, clinical trial. Surgeries were performed at seven medical centres by participating surgeons. Clinical outcomes (Knee Society Score, Range of Motion, WOMAC, SF 12 : and radiographic findings), in addition to postoperative complications, were evaluated with a minimum follow-up of five years. Following data analysis, there were no Significant differences in patient demographics or pre-operative clinical measures between the two groups. At the latest follow-up interval, no Significant differences were found between the CR and PS groups with regard to functional assessment, patient satisfaction or post-operative complications. However the PS group did display statistically Significant improvements in range of motion when compared with the CR group. The results of this investigation would suggest that while comparable in regards to supporting good clinical outcomes, the PS Genesis II design does appear to support significantly improved post-operative range of motion when compared with the CR design

UHMWPE implants are made from small powders which are formed by one of three methods. The powders are either compression molded into sheets and then implants machined from the compression molded material, ram extruded into rods and then machined into implants, or molded directly into the final shape. With each method the powders are exposed to variable temperatures and pressures to consolidate the material. It may not be possible to directly mold some implants such as those with complex geometries or modular locking mechanisms.

Clinical and implant retrieval studies of UHMWPE sterilized by gamma irradiation in air have demonstrated that wear behavior may be influenced by resin type and manufacturing method or both. Directly molded Hi-fax 1900 total knee tibial components were found to have more surface wear (scratching and embedded metallic debris) and less fatigue wear (delamination) than similar components which were machined from ram extruded GUR 415 resin (1). The molded Hi-fax 1900 components also demonstrated less oxidation than the machined GUR 415 components. Both groups of implants were sterilized by gamma irradiation in air suggesting that the resin type and manufacturing method or both may influence resistance to oxidative degradation and associated wear behavior. However, most currently available UHMWPE implants have not been sterilized by gamma irradiation in air and it is not clear if wear behavior of these implants will be affected by resin type or manufacturing method.

During the past five years, much research has focused on the effects of sterilization on UHMWPE wear and mechanical properties. Gamma irradiation sterilization of UHMWPE causes polymer chain scission and oxidation which adversely affects both wear and mechanical properties. However, gamma irradiation can also produce cross linking of the polymer chains which improves wear resistance. Enhanced polyethylenes or highly cross linked polyethylenes have been developed to further improve the wear resistance of the material. Highly cross linked polyethylenes demonstrate markedly improved wear behavior in hip simulator studies, but they also have a decrease in mechanical properties (yield strength, ultimate tensile strength, and fatigue strength). In a highly conforming joint such as the hip where contact stresses are relatively low due to the large surface area of contact, surface wear mechanisms (abrasion and adhesion) predominate while in a less conforming joint such as a fixed bearing knee replacement, where contact stresses are high, fatigue wear mechanisms occur more typically (delamination and pitting). Modifications to improve the wear resistance of UHMWPE such as the highly cross linked materials may therefore be more appropriate for hip replacements than for fixed bearing knee replacements.

Previous efforts to improve the wear behavior of polyethylene such as the addition of carbon fibers (carbon reinforced polyethylene), hot isostatic pressing (Hylamer), and heat pressing have not demonstrated improvements in-vivo. While current joint simulator studies may accurately predict in-vivo wear behavior, clinical studies will ultimately be necessary to determine if highly cross linked polyethylenes enhance the longevity of total joint arthroplasty.

Metal-metal total hip replacements were commonly used in the 1960’s and early 1970’s. Failures usually occurred as a result of aseptic loosening although many of these implants provided long term function similar to metal-UHMWPE bearings.

Metal-metal bearings used in total hip arthroplasty are made of cobalt chrome. The volume of wear generated from a metal-metal bearing is considerably less than that from a metal-UHMWPE bearing. Factors which may affect the metal-metal wear rates include the clearance (difference in radius between the femoral head and acetabular bearing surface), surface roughness, and carbon content of the cobalt chrome alloy. A small clearance provides more contact area between the two surfaces which decreases contact stress while a large clearance permits more fluid flow into the joint. If the clearance is too small, and exceeds manufacturing tolerances, the joint articulation may become excessively tight and equatorial rather than polar contact occurs between the bearing surfaces which can increase frictional torque and cause loosening. This has been implicated as a cause of failure of the McKee-Fararr metal-metal hip replacements. Wear is also increased with increased surface roughness but the effect of other material variables such as cast vs. forged and carbon content are less clear.

Early clinical results with modern metal-metal hip replacements demonstrate clinical results which are comparable to metal-UHMWPE bearings and less aseptic loosening than metal-metal designs used in the 1960’s and 1970’s. However, concerns with metal-metal hip replacements include the generation of metal particulate debris which may travel to the distal sites as well as local osteolysis.

In patients with metal-polyethylene total joint replacements, metal as well as polyethylene particles can be found at distant sites. Urban et al. (1) reported that in a study of postmortem specimens from patients with metal-polyethylene total joint replacements, metallic wear particles were identified in the para-aortic lymph nodes in 68 percent and in the liver or spleen in 38 percent of the patients. The serum and urine levels of cobalt and chromium are elevated in patients with metal-metal articulations. Metals can travel to distant sites in ionic form and little is known about the long term clinical effects of elevated serum and urine metal levels. Cancer risk has not been shown to be increased in patients who have received metal-metal hip replacements. However, long term studies with large numbers of patients are needed to accurately asses this risk.

During the past five years, much research has focused on the effects of sterilisation on UHMWPE wear and mechanical properties. Gamma irradiation sterilisation of UHMWPE causes polymer chain scission and oxidation, which adversely affects both wear and mechanical properties. However, gamma irradiation can also produce crosslinking of the polymer chains, which improves wear resistance. Enhanced polyethylenes or highly crosslinked polyethylenes have been developed to further improve the wear resistance of the material. Highly crosslinked polyethylenes demonstrate markedly improved wear behaviour in hip simulator studies, but they also have a decrease in mechanical properties (yield strength, ultimate tensile strength, and fatigue strength). In a highly conforming joint such as the hip where contact stresses are relatively low due to the large surface area of contact, surface wear mechanisms (abrasion and adhesion) predominate while in a less conforming joint such as a fixed bearing knee replacement, where contact stresses are high, fatigue wear mechanisms occur more typically (delamination and pitting). Modifications to improve the wear resistance of UHMWPE such as the highly crosslinked materials may therefore be more appropriate for hip replacements than for fixed bearing knee replacements.

Gravimetric wear measurements of UHMWPE from hip simulators have been used to predict in vivo behaviour of new materials. However, UHMWPE implants absorb fluid so that measurements of weight loss from wear simulators must be corrected with use of fluid soaked control specimens. There are still some inaccuracies in this technique leading to negative reported wear rates for some highly crosslinked polyethylenes.

The biologic response to particulate debris may be more dependent on the size and number of particles rather than the volume of debris generated. The average particle size appears to decrease with greater amounts of crosslinking suggesting that for some highly crosslinked polyethylenes the number of particles may be greater than for non-crosslinked polyethylene, even though the volume of wear debris is decreased.

Previous efforts to improve the wear behaviour of polyethylene such as the addition of carbon fibres (carbon reinforced polyethylene), hot isostatic pressing (Hylamer), and heat pressing have not demonstrated improvements in vivo. While current joint simulator studies may predict in vivo wear behaviour, clinical studies will ultimately be necessary to determine if highly crosslinked polyethylenes enhance the longevity of total joint arthroplasty.

Skin necrosis after total knee arthroplasty can rapidly lead to infection of the prosthetic components. Risk factors for the development of skin necrosis include rheumatoid arthritis, steroid use, immunosuppression, malnutrition, peripheral vascular disease, and multiple prior scars.

Vascularity of the skin over the knee will affect the rate of healing postoperatively and risk of necrosis. Johnson measured transcutaneous skin oxygen tension and found that the oxygen tension decreases for the first two to three days after surgery and then increases. In addition, the lateral skin edge is more hypoxic than the medial edge. This suggests that when multiple prior scars are present, the most vertical lateral incision should be used to minimise skin hypoxia.

Constant passive motion further decreases skin oxygen tension. Particularly for patients with multiple risk factors for developing wound complications, avoidance or delayed used of early range of motion exercises may be beneficial in reducing the development of skin necrosis.

If skin necrosis does occur after total knee arthroplasty, early recognition of the problem and treatment will minimise the risk of deep infection of the prosthetic components. Necrosis of the proximal wound including the area over the patella may be treated by local wound care and skin grafting. However, necrosis over the tibial tubercle or patellar tendon requires muscle flap coverage to prevent infection involving the patellar tendon. If the patellar tendon is not viable and the extensor mechanism disrupted, the medial gastrocnemius flap can also be used to augment the extensor mechanism. The tendon of the gastrocnemius is repaired to the quadriceps tendon maintaining continuity between the tibia and extensor mechanism.