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This paper presents the first early radiographic and clinical results of trials with the uncemented femoral-neck prosthesis, type Nanos.
In this trial in the Orthopedic Clinic Bayreuth, lasting from June 2004 to May 2006, 45 patients were treated with a Nanos femoral-neck prosthesis. The total number of patients was 45, of which 40 patients returned to our out-patient department for followup examinations. In prospective study were 40 patients (20 men, 20 women) from June 2004 to May 2006 treated with a Nanos femoral-neck prosthesis and followed by regular clinical as well as radiographic check-ups after 3 months (18 patients), 6 months (15 patients), 9 months
(3 patients), 12 months (17 patients), 18 months (4 patients) and 24 months (7 patients). At the time of the operation, their average age was 52,8 years (the youngest patient was 39 the oldest 67 years old). The average height was 1,71 m (min. 1,48m , max. 1,95m). The average weight was 78 kg (min. 52 kg , max. 106 kg). Average Body Mass Index(BMI) was 27,04 kg/m2 (min. 20,20 kg/m2, max. 35,44 kg/m2) and so slightly over the normal range of 20 – 25 kg/m2.
Indications for hip replacement were osteoarthritis by hip displasia (65%), primary arthrosis of the hip (22.5%) or osteonecrosis of the femoral head (12.5%). The evaluation of the medical situation was based on the Harris-Hip- and MerledAubigné-Postel-Scores. Before the operation, the average Harris-Hip-Score of the patients was 56,65 points. After the operation, the average score was 93.7 points after 12 months and 96.8 points after 24 months. The Harris-Scores were classified according to Adolphson (1). Results after 12 months were 88.2 % excellent, 5.8% good, and 5.8 % poor. After 24 months, all seven patients showed excellent results. According to the Merle-dAubigné-Postel-Scores the patients had an average score of 11.3 points before the operation which rose to 17.1 points after 12 months and 17.8 points after 24 months.
Therefore, after one year 88.2% had excellent results, 5.8% good and 5.8% poor results. After two years, 100% (7 patients) had excellent results.
The score results in the multicentral project team (of six other clinics n=175) for the first 12 months after operation are comparable to our own.
The average Harris-Score was here 48.02 points before the operation, 95.92 points after 12 months. According to the Merle-dAubigné-Postel-Scores the patients had an average score of 12.96 points before the operation which rose to 17.77 points after 12 months and are nearly to our own level with 17,1 points. The follow-up examinations showed except for one following case no border-lysis or sings of loosening in the area of prosthesis stems.
In the case of one patient (2.5%) a fissure of the femoral neck was caused when
hammering in the prosthesis stem. Seven to eight months after the operation, the axial movement (migration) was over ca. mobile.
An originally planned corrective operation was later cancelled when the prosthesis stem was proved to be stabled.
In six cases, there were differences in leg-length ≤ 1.5 cm (15.0 %).
Based on densitometric readings, after just three months there was already a noticeable increase in density and after 12 und 24 a clear increase in density on the medial and lateral cortex. Mainly was it in the transition area between the prosthesis stem and the hip of the prosthesis in zone IV/V and I/II (anchoring zone of the prosthesis). There was also a clear increase in density on the lateral cortex in zone II where the prosthesis is mainly supported marking the zones of strong increased forces. These changes are in
accordance with Wolffs Law of Transformation “form follows functions”.
All of the 40 patients operated on described a marked improvement of function and less discomfort in comparison to the situation before the operation.
Only one patient (2.5%) complained of sensitivity to weather changes on the operated side. As 95% of the patients were satisfied with the results within the first two years, there is now a firm indication for the implantation of the Nanos femoral-neck prosthesis in our clinic, especially for younger and more active patients. At the moment, we see no need for modifications of the implant, neither of the surfaces nor of the design.
For the long-term biological stability of the prosthesis besides the patient’s age, the general physical condition and tribology play an important part.
According to our experiences, a BMI ≥ 30 must be considered a contraindication.
On the strength of our results this type of prosthesis together with the implantation technique and taking intra account the necessary indication and contraindication, can be considered a commendable alternative to conventional hip prostheses. 4 mm. The patient now has no problems and with one leg shorter by 4 mm is completelyThe x-rays of one patient - Nr.34 (2,5 %) showed progressive sinking-in of the prosthesis steam.