The main aim of the study was to assess the role of balance control in functional recovery in patients treated using modular knee endoprostheses after bone tumour resection. Although the data collected do not allow an inferential statistical analysis with the necessary power, the relationships studied show some interesting findings from a rehabilitation point of view which should be further investigated by studies using larger samples.
De Visser et al.  had already highlighted the impaired ability in these patients to control a standing upright position compared with that of the healthy population, especially with eyes closed. The results of the present study highlighted a link between these parameters and functional recovery, specifically recovery and performance of gait (speed and resistance): increased difficulty in managing balance is associated with reduced gait performance (10 m-test, 6mwT, TUG). The statistical analyses showed correlations ranging from moderately to strongly significant (Table 2). The same correlation, however, was not found for the level of disability: MSTS score and TESS score do not appear to be associated with the speed of CoP.
Balance control is based on the integration of various sources of information, such as that from visual, vestibular and proprioceptive afferents. This information is necessary for the neuromotor system to be able to realize suitable movement schemes and respond to environmental stimuli. When a patient undergoes wide musculoskeletal resection, this system becomes disturbed and this deficit seems to influence recovery of the best gait performance. Currently, the recovery pathway and treatment methods in the postoperative period are not widely described in the literature and comparative data are limited. In clinical practice, the patient is mainly offered exercises aimed at the recovery of knee articulation and muscle strengthening. For patients with knee endoprosthesis, multiple biomechanical factors may be responsible for reduced stability. Exercises for two-leg standing that progressively become more challenging by modifying the surface or using increasingly unstable surfaces, closed-eye training or dual task exercises, such as throwing a ball and standing in an unstable position, can all be introduced during the rehabilitation process. Balance exercises, not only involving the treated joint but also the entire motor and sensory system, should be encouraged in these patients in order to achieve a better gait performance. Concerning patients undergoing total knee arthroplasty, De Liao et al.  and Piva et al.  showed how rehabilitation programmes that include specific balance exercises can be beneficial in terms of functional outcome (10-m, TUG). According to the data collected, other useful proposals can be advanced in order to plan postoperative rehabilitation.
Strength of the knee extensor muscles was significantly correlated to the MSTS score, whereas no correlation was found between muscle strength and specific gait tests. In Carty’s study , where restored strength was similar (mean 4.15; range 2–5), this correlation was significant both for MSTS and TESS. Benedetti et al.  had already highlighted a lack of correlation between strength of the knee extensor muscles and the biomechanical patterns that the patient was able to develop during gait, by showing that a strength deficit alone does not necessarily lead to a more impaired gait pattern.
In the present study, knee movement in flexion was correlated with MSTS and TESS, however, given the small sample tested, this does not provide a statistical significance. This finding differs from that of Carty et al.  who showed a correlation between joint ROM and TESS. In the present study, 87% of the patients had a ROM of > 90° and the mean flexion achieved was 104° (SD 19, range 75–150), which was in line with levels published by Tsuao (106°, SD 13) , but lower than the 120° (range 85–140) published by Carty . This difference might also explain the different correlation found. At the same time, the lack of association between the range of motion of the knee and specific walking tests is possible since, for normal walking, a knee flexion of 60° is sufficient, which all patients were able to reach. For professionals who deal with the functional recovery of oncological-orthopaedic patients, rehabilitation should not be aimed just at improving a specific deficit, such as muscle strength or joint ROM, but also exercises based more on complete gait patterns where proprioceptive stimulus is a central element.
In the present analysis we also examined some elements that cannot be modified directly during the course of treatment, but should be borne in mind by the clinician for a better understanding of the progress of a patient’s recovery. Moreover, the duration of chemotherapy and patient age are factors that can influence gait resistance and a patient’s perception of autonomy, respectively.
Though this study presents some novel findings, there are limitations to consider, mainly, the study uses a small sample size, thus excludes the opportunity of a more in-depth statistical analysis. The rarity of this disease is one element that significantly influences the possibility to design research protocols on larger and more uniform samples to be able to perform multivariate statistical analyses. For this same reason, patients undergoing distal femur and proximal tibia resection were included in the observation group, even though their reconstruction features have different biomechanical and anatomical elements. Only 3 out of 15 patients were found who underwent proximal tibia resection. Finally, the evaluation of the postural control included the measurement of the speed of the CoP with a stabilometric platform. The authors’ choice to carry out a test lasting 10 s is a limitation of the study, even if in the literature the execution of this measurement is not uniform and it is not possible to define a standard mode of execution. Furthermore, the authors hypothesize that the average speed of CoP is partially affected by the duration of the test itself.
According to the present authors, however, the data examined still provide useful indications to guide physiotherapy treatment of these patients and may be able to guide the way for future research in this field.