Seven fresh frozen humeri from geriatric female donors were instrumented with the proximal humerus interlocking system (PHILOS) plate and placed in a 37 ¡ãC water bath. Thereafter, four proximal perforated screws were augmented with 0.5 ml PMMA each. During augmentation, the temperatures in the subchondral bone and on the articular surface were recorded with K-type thermocouples. The measured temperatures were compared to threshold values for necrosis and apoptosis of bone and cartilage reported in the literature.
The heat development was highest around the augmented tips of the perforated screws and diminished with growing distance from the cement cloud. The highest temperature recorded in the subchondral bone reached 43.5 ¡ãC and the longest exposure time above 42 ¡ãC was 86 s. The highest temperature measured on the articular surface amounted to 38.6 ¡ãC and the longest exposure time above 38 ¡ãC was 5 min and 32 s.
The study shows that augmentation of the proximal screws of the PHILOS plate with PMMA leads to a locally limited development of supraphysiological temperatures in the cement cloud and closely around it. The critical threshold values for necrosis and apoptosis of cartilage and subchondral bone reported in the literature, however, are not reached. In order to avoid cement extravasation, special care should be taken in detecting perforations or intra-articular cracks in the humeral head.