Introduction

Three-dimensional (3D) printing is a precise method of reproducing complex structures. Orthopaedic surgeons may utilize 3D imaging to better plan procedures, design implants, and communicate with other providers and patients. However, one of the limitations of 3D printed models has been the high cost associated with third-party creation of such tools. With the recent increases in the use of 3D printing many publically available software programs have been developed, which allow for inexpensive office-based production of models. We present a simple, inexpensive technique which can be used by surgeons for the rapid fabrication of 3D models in-office.

A new hinge knee system (LEGION HINGE, Smith & Nephew, Memphis, TN) was designed to treat gross knee instability resulting from loss of collateral ligament function, femoral and/or tibial bone loss, or from comminuted fractures of the proximal tibia or distal femur. The knee system is offered with an insert that guides the motion of the implant for kinematic improvement. The purpose of this study was to evaluate kinematic and wear performance of this novel hinge knee replacement system.

The kinematics and kinetics of the Guided Motion (GM) hinge knee were assessed for a deep knee bend using a numerical lower leg simulator. Measurements of A/P translation and I/E rotation were compared to 3D MRI data of healthy weight bearing knees and measurements of M/L patella shear forces were compared to a standard primary knee implant. Three GM knee systems were tested for wear performance. All metal components were fabricated from cobalt chrome except for the Ti-6Al-4V insert locking screw. All plastic components were fabricated from UHMWPE. Wear testing was conducted on an AMTI 6-station force controlled knee simulator for approximately 5 million cycles under ISO 14243-1 load/motion profiles and soft tissue constraints. Simulation results showed that up to 130° of flexion the anterior/posteror (A/P) translation and internal/external (I/E) rotation followed a similar path over the flexion range compared to the MRI data. The magnitude of A/P translation at 130° was 9.5 mm for the GM design compared to 15.7 mm for the MRI data. The magnitude of I/E rotation at 130° was 18° for the GM design compared to 20.8° for the MRI data. The GM design showed a maximum M/L patella shear force of 456.8 N compared to 1152.4 N for a standard primary knee design over the flexion range. All constructs successfully completed wear testing and were fully functional with no issues for binding of the mating parts. All polyethylene components showed only burnishing on the articulating surfaces. The volumetric wear rate of polyethylene components was 17.54±1.24 mm3/Mcycle. The volumetric wear rate of the metal components (excluding femoral and tibial tray) was 0.045±0.01 mm3/Mcycle.

Testing showed the GM design has A/P and I/E kinematics that are similar to those seen in a normal healthy knee and good patella tracking as evidenced by the low M/L patella shear forces. The wear rate of the polyethylene parts was within the range of wear rates published in the literature for primary knee designs (up to 35.8 mm3/Mcycle). The low metal wear rate indicates that fretting and corrosion of the components was minimal.

We conclude the GM design more closely replicates the kinematics of the natural knee without compromising the wear characteristics. This could lead to better outcomes for the patient population that requires a hinge knee implant.

There has been a longstanding need for a structural biomaterial that can serve as a bone graft substitute or implant construct and is effective for fixation by bone ingrowth. A porous tantalum material was developed to address these issues. The purpose of this paper and presnetation is to describe the properties and 2 to 5 year clinical results of porous tantalum in various reconstructive orthopaedic procedures.

Porous tantalum has been used to manufacture primary and revision acetabular cups, acetabular augments, tibial and patella implants, patellar augments, structural devices for the treatment of osteonecrosis, and spinal fusion implants. Clinical follow-up includes: 2–5 year clinical and radiographic evaluation of: 414 monoblock cups in primary THA, 36 monoblock cups and 587 revision hemispheres used in revision THR, 16 hips revised with acetabular augments and revision hemispheres; 2 to 4 years for 101 tibial implants used in primary TKR and 69 patellas used in cementless TKR; 2–4 years for 11 patellar augments in salvage TKR, 1–5 years for 53 revision TKRs using knee spacers; 1–4 years for 91 osteone-crosis hip implants; and for 15 cervical fusion cases.

This innovative tantalum implant material with trabecular architecture possesses advantages in stiffness, friction coefficient, porosity, rate and extent of tissue ingrowth, and versatility in manufacturing of structural devices. It has been clinically validated in numerous and diverse reconstructive procedures.

Hypersensitivity to metal alloy orthopaedic implants has become identified increasingly as a cause of implant failure. Because of their hypoallergenic properties, ceramic materials have been recommended as an alternative to metals. Unfortunately, the cost of ceramics and limitations imposed by their material properties has restricted these applications. The metalloceramic composite Oxinium® has been suggested as asubstitute. This is the first study to prospectively compare these materials in patients with documented cobalt-chrome hypersensitivity.

Over a period of ten years, preoperative screening using skin patch testing and in vitro leukocyte stimulation testing of patients with gonarthrosis and a history of metal hypersensitivity identified sixteen patients with allergy to cobalt-chrome alloy. Twelve (all& ) underwent primary, and four underwent revision (3& , 1%) knee replacement surgery using either alumina ceramic femoral components (3 primary, 2 revisions) or Oxinium® femoral components (9 primary, 2 revisions) All implants were fixed with acrylic cement, and all-polyethylenetibial implants were used in each procedure.

None of the patients in the primary groups developed symptoms of allergic reaction at a minimum of one year following surgery. Serial serum antibody and leukocyte stimulation studies have shown no reaction following placement of either type of prosthetic knee. Those undergoing revision surgeries had rapid resolution of preoperative symptoms of pain, effusion and eczematous rash. Serum studies showed a concomitant fall inantibody levels. The two patients undergoing revision surgery with alumina femoral implants subsequently underwent second revisions (both at 8 years) using Oxinium® femoral implants. Neither developed clinical symptoms orchanges in antibody profile.

While the number of patients in the present study is relatively small, it is the only independent, prospective, clinical comparison of these materials. The uniformly good results suggest implants of Oxinium® offer the hypoallergenic properties of alumina without adverse-material properties and at a lower cost.

Revision TKA patients who have severe patellar bone loss or undergo patellectomy often have inferior clinical results. Current treatments are limited and often unsatisfactory. This study reports the surgical technique and clinical follow-up (4-year minimum) for 10 patients who underwent revision or salvage TKA and received a porous tantalum implant for replacement of their patella.

The prosthesis is comprised of two parts, a poroustantalum base and titanium suture ring for initial fixation, and a polyethylene surface that is cemented to the base. The surgical technique evolved over the course of the first three cases, during which the suture technique and size (non-absorbable number 2) and bone preparation were defined.

The results of this study indicate that this porous tantalum patella is an effective prosthetic option that is capable of improving function and reducing pain for patients with severe patellar boneloss and complicating factors.