Total knee arthroplasty has been shown to be a reliable method of treating various types of arthritis of the knee. 5,6,8,16,23 At one time the indications for total knee arthroplasty were limited to older, more sedentary patients. 6 Today, more demanding patients are requiring total knee arthroplasties at younger ages for posttraumatic, degenerative, and rheumatoid conditions. Advances in technology, materials, and designs have allowed for more predictable results and the creation of longer lasting materials. 14,16,17 The goals of total knee arthroplasty are pain relief, improved function, correction of deformity, and the accommodation of an active lifestyle, especially in younger patients. The results of total knee arthroplasty for older patients are well-documented in the literature, but the data for younger patients remains sparse. 21–23
Recently, Hofmann et al 16 reported excellent 10- to 14-year results in a group of active patients. This study group represented a broad age range of patients who received a metal-backed patella 10 and an asymmetric tibial tray. Postmortem confirmation of extensive skeletal attachment by bone ingrowth also was done. 2–4 The purpose of the current study was to evaluate the clinical results of cementless total knee arthroplasty in a group of patients, 50 years or younger. It was hypothesized that the clinical results would support the durability of porous-coated fixation using an asymmetric tray, a metal-backed patellar component, and a femoral component with a deep trochlear groove.
MATERIALS AND METHODS
Between 1986 and 1998, 75 primary cementless total knee replacements in 57 patients 50 years or younger were done. All surgeries were done by one surgeon (AAH). The Natural Knee™ system (Sulzer Orthopedics, Inc, Austin, TX) was used for all patients (Fig 1). This design has a cancellous structured commercially pure Ti porous-coated surface, with a mean pore size of 530 μm and a porosity of 55% abutting host bone. All replacements were inserted using a cementless technique with autograft bone chips. 15,16 The decision to use a cementless technique was made intraoperatively based on the quality of bone. A standard technique and postoperative protocol was used for all patients. 2,10,16 Preoperative and postoperative knee scores were recorded using a 100-point modified Hospital for Special Surgery knee scoring system that takes into account pain, motion, stability, and strength. 10,16 The Knee Society clinical rating system also was used to evaluate patient function and knee assessment on a 100-point scale. 20 The bone-implant interface was assessed with radiographs and evaluated for any radiolucencies or evidence of loosing. Preoperative and postoperative alignment were measured from 52-inch long radiographs taken with the patient standing. Failure was defined as revision of the femoral, patellar, and/or tibial component attributable to aseptic loosening. Polyethylene exchange for wear or instability was not considered a failure because this was not a result of loss of fixation.
Seventy-five knee replacements in 57 patients comprised the study group. There were 35 left knees and 40 right knees. The average age of the patients was 42 years (range, 31–50 years). Followup averaged 111 months. There were 24 men and 33 women. The average weight of the patients was 205 lb (range, 109–320 lb). The primary diagnoses were posttraumatic arthritis in 27 patients, osteoarthritis in 17 patients, and rheumatoid arthritis in 19 patients. Additional diagnoses included gout in two patients, hemophilia in two patients, juvenile rheumatoid arthritis in four patients, lupus in one patient, von Willebrand’s disease in one patient, osteochondritis dissecans in one patient, and pigmented villonodular synovitis in one patient.
The preoperative modified Hospital for Special Surgery knee scores were 67 points (range, 40–81 points) and postoperative score was 97 points (range, 85–100 points) at last followup. Knee Society scores averaged 67 points (range, 55–80 points) for knee assessment preoperatively and 98 points (range, 85–100 points) postoperatively. Patient function was 56 points (range, 45–70 points) preoperatively and 95 points (range, 72–100 points) postoperatively. Preoperative range of motion (ROM) was 5° to 106° and postoperative ROM was 2° to 113°.
Radiographic analysis was done by using The Knee Society radiographic evaluation system. 11 There were no progressive radiolucent lines and all lines were less than 1 mm. The femur had four radiolucencies in Zone 1, one each in Zones 2 to 4, two in Zone 5, and none in Zones 6 and 7. The tibia had eight radiolucencies in Zone 1, four in Zone 2, one in Zone 3, six in Zone 4, one in Zone 6, and none in Zones 5 and 7. The patella had one radiolucency in Zones 1, 2, and 4. There were no radiolucent lines in Zones 3 and 5.
Fifty-two-inch long anteroposterior (AP) radiographs, taken with the patient standing, were used to evaluate the preoperative and postoperative femorotibial angles. Preoperatively, femorotibial angles measured 5.5° ± 6.3° valgus (range, −8°–22°). Postoperatively, the femorotibial angles measured 6.6° ± 1.4° valgus (range, 4°–9°).
There were two infections and 12 polyethylene exchanges (seven for instability and five for wear). There were 32 posterior cruciate ligament-substituting ultracongruent polyethylene inserts and 43 posterior cruciate ligament-retaining congruent polyethylene inserts. Of the seven exchanges for instability, four were for posterior cruciate ligament insufficiency and three were for laxity. The average thickness of the 75 polyethylene components was 11.5 mm (9 mm of polyethylene) and the average thickness of the exchanged polyethylene was 11 mm (8.5 mm of polyethylene). The average time for wear revision was 7.5 years. There were no revisions for loosening or loss of implant fixation. There were 24 manipulations with the patient under anesthesia for poor postoperative ROM. There was a correlation between prior knee surgeries and the need for a manipulation. Fifteen of the 24 patients who had manipulation had multiple (two or more) surgeries (arthroscopy, anterior cruciate reconstruction, high tibial osteotomy) before their index total knee replacement. The average number of prior surgeries for the patients who had a manipulation was two.
Fifty-two of the 75 knees had the patella resurfaced and 23 were unresurfaced. Of the knees with a resurfaced patella, three (5.8%) had the metal-backing and the damaged insert revised for polyethylene failure and a newly-designed metal-backed component with a larger polyethylene insert implanted. Two (3.8%) had just a polyethylene exchange of the patella component without removal of the metal backing. Three (13%) of the 23 unresurfaced patellas had an eventual resurfacing because of anterior knee pain.
The results of this retrospective study show the excellent fixation survivability of cementless total knee replacement for younger active patients. The concern of increased loosening rates, and the need for multiple revisions have discouraged the use of cemented total knee arthroplasty in the younger patient. 8 Despite this, the indications for total knee arthroplasty have expanded over the years to include younger, more active patients. The main advantage of using a cementless technique is that if a revision is required in the future, excessive amounts of bone are not lost when the prosthesis is removed. 2,10 The success of the Natural Knee™ prosthesis is well-documented in the literature. 1,16,18 Some cementless designs have reported a higher rate of loosing and revisions. 9,12 Aseptic loosening caused by the absence of bone ingrowth has not been the case with this design. 2–4,10,16
Dalury et al 7 reported on 103 cemented total knee replacements in patients younger than 45 years. The average followup was 7.2 years. In contrast to the current study, the majority of the patients reported on by Dalury et al had a diagnosis of rheumatoid arthritis (87%). There only were three revisions (two patellar failures and one infection), but none were for loosening. Although this study shows good results, the majority of patients were sedentary and less demanding on the fixation.
Diduch et al 8 reported on 108 cemented total knee arthroplasties in patients younger than 55 years. The average followup was 8 years. The patients in this series all had the diagnosis of osteoarthritis or posttraumatic arthritis similar to the current patients. They had an overall survival rate of 94%. Gill et al 13 reported 68 cemented total knee arthroplasties in patients who were 55 years or younger. Their average followup was 9.9 years and there were two revisions for aseptic loosening and one for infection. Although these two studies have similar results to the fixation achieved in the current study, the clinical advantage of the porous-coated device is the bone-sparing characteristic of the porous-coated design at the time of revision.
The implant design and type of porous coating is critical to achieving durable fixation in cementless total knee arthroplasty. Firestone et al 12 reported a 6% failure rate in the PCA porous-coated design caused by fixation failure. Fixation failure did not occur in any of the patients’ components in this series.
As with previous cementless devices, the initial design used in the current study was limited by thin and flat polyethylene similar to that reported previously. 12,19 New cementless designs have been adapted to take into account the conformity and thickness required in tibial insert design to prevent early polyethylene failure and catastrophic wear.
It is interesting to reflect on the number of manipulations required in the current patients. Additional studies are required to better understand the relationship between prior knee operations and the need for manipulation. A previous investigation by Hofmann et al 16 using this design did not have the higher manipulation rates observed in this younger group of patients. Therefore, the requirements for manipulation do not appear design-related. Issues of soft tissue contracture need additional investigation to reduce the manipulation rate in the patients with previous knee surgeries.
There is literature to support the use of cement and cementless techniques for the younger patient population. 7,13,16,24 The risk of bone loss and implant loosening with the use of cement have led many to use cementless techniques for younger more active patients. The current study shows the reliability and durability of cementless fixation in total knee arthroplasty for the young patient. The weak link in this study was the polyethylene (no loose tibias, femurs, or metal-backed patellas). The polyethylene experiences high load demands by young, active patients, which was shown by the 12 insert exchanges and five patellar revisions attributable to wear and instability. The more conforming polyethylene (ultracongruent) was found to be more durable and stable. The new highly cross-linked polyethylene and alternative bearing surfaces may allow for longer component survival and less revisions attributable to polyethylene failure in the future.
The authors thank Dr. Roy D. Bloebaum for editorial review and Gwenevere Shaw for contribution in manuscript preparation.
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Richard S. Laskin, MD—Guest Editor