Varus or Valgus malpositioning of tibial prosthetic components in total knee replacement (TKR) surgery may lead to early failure due to increased polyethelene wear, soft tissue imbalancing, aseptic loosening and eventually revision surgery. Therefore, the clinical success of total knee arthroplasty (TKA) correlates with good component alignment. Conventional methods of coronal tibial alignment result in an acceptable range of prosthetic alignment in relation to the anatomical axis (tibial tangent angle). The measurement ranges from 90° ± 3°, but literature quotes that there is up to 27% of cases with coronal tibial alignment deviation of greater than 3°. Many studies show that the use of conventional intramedullary rod alignment versus extramedullary rod alignment gives similar results. The tibial alignment and overall prosthetic alignment in TKA has improved remarkably by using computerized navigation assisted surgery (CAS), with tibial tangent angle of 90° ± 3 in up to 97% of cases. However, the success of accurate tibial and femoral alignment depends on the surgeon and the data fed to the computer. Also long term results on survival rates of TKR using CAS is still pending. It is clear that assessing tibial alignment (ie. anatomical axis) with whatever method used faces challenges which will affect the tibial bony cuts and the final tibial tangent angle. To achieve a 90° tibial cut in relation to the anatomical axis we made use of fluoroscopy intra-operatively to assess the anatomical axis of the tibia and the correct alignment of the tibial cutting block. TKR's were performed on 36 consecutive patients over a 4 month period. The aim was to assess the coronal tibial alignment of the tibial component intra-operatively using fuloroscopy. A conventional manual extramedullary alignment rod with its tibial cutting block was used and the final positioning was confirmed with an image intensifier. The tibial cutting block must be at 90° to the anatomical axis of the tibia. The rest of the TKR procedures were performed as routinely described. Post-operative radiographs were taken on the same day as the surgery and again at six week follow up visit when the tibial tangent angle was measured.Background:
Methods:
Over five years, 85 low-cost primary total arthroplasties (Eortopal Bulteamex) were done at a referral hospital. These were followed up for a mean of 48 months (minimum of 18 months). There were 11 revisions (13%), with four (4.7%) necessary for aseptic loosening, two (2.3%) for recurrent dislocations, four (4.7%) for sepsis and one (1.3%) for a periprosthetic fracture. When these results were compared with the Trent Regional Arthroplasty Register, the revision rate was noted to be four times higher than in the Trent study, with aseptic revisions being twice as high and infection rates three times higher. Dislocation rates were half those in the Trent study. We concluded that our lower dislocation rate probably reflected the quality of our surgery. Our higher sepsis rate was probably related to the hospital environment, and the high aseptic loosening rate due to the quality of the ‘low-cost’ prosthesis. We conclude that to be cost-efficient, ‘low-cost’ pros-theses must be of good quality and that the hospital environment must be optimal. This study highlights the need for an Arthroplasty Register in South Africa.
Four low-cost hip prostheses, explanted because of clinical failure within three years, were subjected to a retrieval analysis study to determine the cause of the early failure. The study aimed to determine whether the low-cost prosthesis was substandard and had consequently contributed to the need for early revision. The retrieval analysis included a photographic record, a fractographic examination, an analysis of the material composition of the components, and a mechanical property analysis. These investigations were done in accordance with the ASTM F561 standards. Results demonstrated substandard qualities in respect of all parameters analysed. We conclude that the inferior quality of these low-cost hip prostheses contributed appreciably to their early failure and revision.
