Mechanical stability of the stem is believed to be an important factor in successful impaction grafting in revision THA. We asked whether particle size, femoral bone deficiencies, stem design, graft composition, and impaction technique influenced the initial stability of the stem in vitro using model femora and human bone particles. Bone particles made with a reciprocating blade-type bone mill contained larger particles with a broader size distribution than those made by a rotating drum-type bone mill and had higher stiffness on compression testing. The stiffness on torsional testing decreased as the degree of proximal-medial segmental deficiencies increased. The stiffness and maximum torque in a stem with a rectangular cross section and wide anteroposterior surface were higher in torsional tests. Adding hydroxyapatite granules to the bone particles increased the torsional stability. To facilitate compact bone particles, we developed a spacer between the guidewire and modified femoral packers. This spacer facilitated compacting bone particles from the middle up to the proximal and the technique increased the amount of impacted bone particles at the middle of the stem and also improved the initial stability of the stem. Stem design and degree of deficiencies influenced stiffness in the torsional test and the addition of hydroxyapatite granules enhanced torsional stiffness.

In revision THA with bone defects, impaction bone grafting is one proposed solution. Morsellized allografts are commonly used, however allograft has some disadvantages. We tried to use hydroxyapatite (HA) granules in stead of morsellized allografts. Three types of HA granules were prepared. To facilitate the manipulation of HA granules, we tried to add arginine amino acid as glue. These granules were impacted into the plastic femoral canal and collarless polished tapered stem was fixed with PMMA bone cement. Cyclic compression test and torsional test were performed using an Instron type mechanical tester. Mechanical stability of the stem fixed with HA granules for impaction grafting was superior to morsellized allografts. Adding arginine amino acid to HA granules, impaction technique became easier and the initial stability of the stem was improved.

The effect of self-quarantine and avoiding non-essential outings due to COVID-19 on the symptoms of patients with lumbar spinal stenosis (LSS) remains unknown. In this prospective study, patients with LSS who self-quarantined from baseline (SQ group; 80 patients) were matched to controls who did not self-quarantine (non-SQ group: 60 patients), based on age, gender, medication, activities of daily living (ADL), and low back symptoms. The change in low back symptoms, ADL, and health-related quality of life (HRQoL) between baseline and follow-up (after self-quarantine periods) were compared between the groups. Compared to baseline, the NRS score for low back pain at follow-up in SQ group significantly improved, but not in non-SQ group. No significant difference was found regarding changes in leg pain or numbness. Low back pain improvement did not lead to ADL improvement. The Short Form 12 evaluation revealed the role/social component score in SQ group to be lower than that in non-SQ group at follow-up; no difference was found for the physical or mental components. This study revealed self-quarantine with conservative treatment accompanied short-term low back pain improvement in patients with LSS. It might help to understand the situation in the spine department during the COVID-19 pandemic.