The most important finding of this study was that the mean graft tension of 24 N during surgery to restore the patellofemoral relationship was much greater than the graft tension of 2 N in previous laboratory cadaveric studies [11], and that our surgical restoration of patellofemoral joint stability in patients with recurrent patellar dislocation and patellofemoral ligament reconstruction using a tensiometer was a more accurate and safer way to achieve satisfactory treatment results.
The use of patellofemoral ligament reconstruction to address patellar instability has become an effective modality [2, 2, 8, 10, 22, 24, 25], but the approach to graft tension remains controversial and, in general, clinical outcomes are promising when performing MPFL reconstruction using various methods of controlling graft tension (Table 4).
Gaining the proper graft tension can be a challenge and requires the surgeon's experience to assess the graft tension during the procedure.Beck [11] and Stephen [17] believe that For a graft tensioned to 2 N, anatomically positioned MPFL reconstruction restored intact medial and lateral joint contact pressures and patellar tracking.Philippot [18] argues that Only 10 N of graft tension could restore normal patellar tilt, lateral shift and rotation.Using a digital tensiometer and using the same method, we found that a force of 2N or 10N during surgery did not restore the normal patellofemoral track and that an average force of approximately 24N was required to restore the correct patellofemoral track.However, it does not mean that the ligament tension is 24N in all patients, this value is only the average value, we have performed surgical procedures with a maximum of about 32.5N and a minimum of about 15.3N, while as Ackermann [26] argued Femoral interference screw insertion significantly increases graft tension in MPFL reconstruction.In contrast to frozen cadaver studies, factors affecting tension during surgery include the depth of the patient's grade of anesthesia, the strength of the quadriceps muscle, the strength of the lateral retinacular, the tension of the skin and fascia, and the friction between the graft and the bone tunnel, all of which can affect graft tension.But the most significant influencing factor is the tension of the lateral retinacular and the friction of the graft-bone tunnel, which we believe Medial patellar glide (MPG) test less than one quadrant indicated lateral retinacular tightness.Lateral retinacular release is recommended at this point. MPG of four quadrants indicated medial patellar subluxation[19].The diameter of the graft-bone tunnel is separated by 1 mm, so that the graft-bone tunnel friction is constant for all patients.
Over tension of the graft may actually be more common than actually believed, and surgeons in their efforts to achieve a smaller patellar tilt angle and patellar congruence angle post-operatively may excessively increase graft tension, increasing medial patellofemoral joint contact pressure, which in turn can lead to the later development of patellofemoral arthritis or chondromalacia patellae in patients.We consider that that the native MPFL acts principally as a checkrein and not a tensioner, Clinically,Thaunat and Erasmus suggested the similar medial and lateral movements to contralateral patella as a reference for tensioning the graft[20].Zumbansen et al [21] used extracortical clamping as femoral hybrid fixation, in order to rule out influence of the measurements due to graft slippage.Erickson et al [22] determined the tension of the graft by medial and lateral movement of the patella and ROM.Niu et al [23, 24] fixed the femoral ending, then the patellar end, and after determining the appropriate tension arthroscopically, fixed the patellar end of the graft tail through an extracortical clamping, thus reducing the slippage of the graft and fluctuations in tension.However, it is most commonly used clinically to observe the patellofemoral joint relationship by arthroscopic flexion of the knee at 30°, while the lateral femoral assistant pulls the graft tail and adjusts the graft tension [8, 9].We believe that the use of tensiometer pulling instead of assistant pulling results in more stable and accurate graft tension, reduces manual fluctuations and reduces over-loosening or over-tightening of graft tension during surgery.Tightening the MPFL graft may create an overload of patellofemoral cartilage, restrict the range of motion and result in a postoperative loss of knee flexion [11、12]. In contrast, patellar instability can exist continuously, and patellar dislocation can even recur [17].
This study has the following advantages: we have reviewed the relevant surgical modalities, we have used for the first time a digital tensiometer for patellofemoral ligament reconstruction during surgery, and we have provided a more accurate figure to quantify graft tension and even to determine whether there is excessive medial patellofemoral pressure by reflecting the magnitude of graft tension laterally.Secondly, it fundamentally reduces the risk of human-induced changes in graft tension during surgery, a detail that is easily overlooked in previous procedures and which can affect outcomes and complications.Limitations of the study include firstly, the small sample size and medium-term follow-up and the absence of a reference group, mainly because the majority of patients with patellar dislocation have bony structural abnormalities, but most of these patients meet the exclusion criteria. This approach therefore requires a larger sample size and long-term follow-up.Secondly, due to the impact of the COVID-19 virus, some patients opted for follow-up by telephone, where the patient's post-operative knee function score is influenced by the patient's subjective perceptions. Thirdly: when selecting our inclusion and exclusion criteria, we considered congenital developmental abnormalities as an important factor affecting prognosis, so we included patients with congenital development as an exclusion criterion, thus avoiding some of the high-risk factors.