The Study Of 3D Printing Assisted Modified Lateral Arc Approach For Displaced Intra-articular Calcaneal Fractures

The best treatment for displaced intra-articular calcaneal fractures(DIACF)remains one of the greatest challenges faced by orthopedists,who account for 75% of all calcaneal fractures and 4% of systemic fractures,and are associated with unpredictable,relatively poor clinical outcomes.For more than 170 years,the DIACF has experienced the debate of conservative-surgical-conservative-surgical treatment,and the optimal treatment options have been the subject of controversial discussion.In addition to the irregular shape and complex anatomical structure of the articular surface,the unique and fragile soft tissue covering of the lateral calcaneus makes the surgical treatment of calcaneal fractures a real challenge for surgeons.In the last 20 years,a large number of clinical studies has favored surgical intervention and demonstrated that the restoration of the anatomic structure of calcaneus can bring clinical satisfactory long-term effects.Since the 1990 s,extended lateral approach(ELA)has been considered as the gold standard for the treatment of DIACF.However,it has as high as 20%~37% of the wound complications.Many authors believe that the benefits of surgery cannot offset the injuries caused by complications and choose conservative treatment.In recent years,more and more researchers have found that the exposure of the vertical arm of ELA and incision suture are easy to damage the lateral calcaneal artery(LCA),which supplies the blood of the flap.After iatrogenic LCA injury,ischemic complications are easy to occur which results in delayed wound healing,incision dehiscence,skin flap necrosis,incision infection,etc.Another difficulty with DIACF treatment is the difficulty of achieving stable fixation.Essex-Lopresti suggested that the calcaneal fracture mechanism is a vertical violence that causes the lateral margin of the talus to collide with the calcaneus,resulting in an initial fracture line that extends laterally and then forwards medially and dividing the calcaneus into 2 major parts,the posterior lateral mass and the sustentaculum tail bone mass.The sustentaculum tail bone mass is also known as a “constant bone mass”,which is surrounded by the attachment of the triangular ligament,the plantar ligament(spring-loaded ligament),and the intercalar ligament.It's position is relatively constant,so as to the role of reset template.Therefore,the precise fixation of the sustentaculum tail bone mass is essential to restore the anatomic structure and biomechanical stability of the calcaneus.However,only relying on the anatomical experience of surgeons,the success rate of accurate insertion of the sustentaculum tail screw is not high enough.The wrong implantation will damage the nerve vascular bundles and tendons around the sustentaculum tail,and the sustentaculum tail screw in the protruding joint will lead to severe subtalar arthritis or even inability to walk.Therefore,it is of great significance to reduce the incision complications and improve the placement rate of sustentaculum tail screws.In this study,we propose a modified lateral arc approach without LCA damage(from external ankle and Achilles tendon lateral horizontal edge node,into 150° arc to red and white line,along the red and white line to reach the fifth metatarsal base 2 cm proximal arc forward again).The safety of the incision was verified through autopsy of the cadaver specimen,bidirectional Doppler flow detector and color Doppler ultrasound,and a new idea was provided to assist sustentaculum tail screw positioning with the help of customized 3D printing guide plate.Objective:The safety of the modified lateral arc approach was verified by autopsy,bidirectional Doppler flow detector and color Doppler ultrasound to locate the LCA shape.The 3D printing guide plate was used to locate the sustentaculum tail screw and determine the best position of the steel plate and the height and Gissane angle after fracture reduction,so as to reduce the incision complications and stable fixation of the calcaneus.Methods:1)The fresh frozen corpse of 6 cases of calf-foot was thawed and perfused with red latex.Mark the modified lateral arc approach and the lateral malleolar tip(LMT).Distance 1(the distance between LMT and LCA on horizontal line),distance 2(the distance from LMT to LCA on 45° line),distance 3(the distance from LMT to LCA on vertical line)were measured.Then observe if the incision passed through the LCA trunk.2)The LCA position of 12 patients with calcaneal fractures before and after dissecting were measured by bidirectional Doppler flow detector.Modified lateral arc approach was marked before measurement.Since the LMT down,horizontal line,45°line,vertical line were drew.The vascular pulse was found along 3 lines.The relationship between the pulse point and the incision was determined.3)The vascular diameters of LCA of 10 healthy volunteers were measured by Color Doppler ultrasound,and the relationship with the location of improved incision.Modified lateral arc approach was marked before measurement.Since the LMT down,horizontal line,45° line,vertical line were drew.Distance 1(the distance between LMT and LCA on horizontal line),distance 2(the distance from LMT to LCA on 45° line),distance 3(the distance from LMT to LCA on vertical line),and the diameter of LCA on LMT horizontal line were measured.4)38 cases with unilateral calcaneal fractures were made retrospectively analysis.They were divided into the conventional surgery group and the 3D printing group according to whether or not to use 3D printing,and the differences between the two groups in incision complications,sural nerve injury,operation time and postoperative AOFAS score were compared.5)The 3D printing group imported the Dicom data of bilateral calcaneal CT scan through Mimics software.The original image before the fracture of the affected calcaneus was mirrored from the image of the healthy calcaneus.The calcaneal guide plate was designed by commands such as dilution,spliting,analysis and Boolean calculation,and was printed with 3D printer as 1:1 to guide sustentaculum tail screw.Results:1)LCA trunks were all located on the back side of modified lateral arc approach.The trunk of LCA in 4 cases did not pass through the modified lateral arc approach.The LCA trunk of the 2 specimens passed through part 2 of the modified lateral arc approach.Distance 1 was 30.715±3.418 mm.Distance 2 was 31.032±1.898 mm.Distance 3 was28.897±1.833 mm.2)The overall detection rate of 72 points in 12 patients with calcaneal fractures was86.1% by bidirectional Doppler flow detector.All detected pulsating points were located on the dorsal side of modified lateral arc approach.3)LCA was detected by color Doppler ultrasound in the horizontal line of LMT,45°line and vertical line.The diameter of LCA on the left and right side at LMT was1.450±0.280 mm and 1.470±0.250 mm,respectively.The distance 1 on the left and right side was 31.567±2.567 mm and 31.453±2.161 mm,respectively.The distance 2 on the left and right is 30.257±1.758 mm and 30.364±2.010 mm,respectively.The distance 3 on the left and right is 30.228±1.179 mm and 30.370±1.060 mm,respectively.LCA showed a high consistency of decreasing amplitude from the starting point to the fifth metatarsal base.On prominence of the medial malleolus level,three-phase waves were seen on bothsides in 6 postulants,while dual phase and single phase wave were dominant on 45° line and vertical line.4)Only 1 patient in the conventional surgery group had delayed wound healing without skin flap necrosis,superficial infection and deep infection.Sural nerve damage occurred in 4 cases(10.5%).There were 1 case in the conventional operation group and 3cases in the 3D printing group,and no significant difference was found between these two groups(p<0.05).5)The two groups were statistically significant in terms of operation time and AOFAS score(p<0.05).And the operation time of the conventional surgery group was109.524±25.734 min,while the operation time of the 3D printing group was93.824±15.962 min.The AOFAS score was 81.191±12.456 in the conventional surgery group and 87.824±5.114 in the 3D printing group.6)Subgroup analysis: The AOFAS score of litigation indemnity group was88.533±5.249,and it was 81.304±11.822 of non-litigation indemnity group.The difference between the two groups was statistically significant(p<0.05).However,the litigation indemnity group had longer hospital stays with value of 20.800±4.195 days.The non-litigation indemnity group had was 16.913±4.430 days.There were statistical significances between 2 groups in this item(p<0.05).7)Subgroup analysis: The AOFAS scores of Sanders II type,III type and IV type were 88.600±3.043,86.000±3.850,64.200±17.355 respectively.There were statistical significance between Sanders II type and III type patients(p<0.05).There were much higher statistical significance between Sanders IV type and II type patients(p<0.05).Conclusion:1)The modified lateral arc approach designed by us can avoid LCA injury,and the arc designed to remove the corner has a relatively wider pedicle,more blood flow for the flap,and lower incision complications.2)The 3D printing guide plate designed by us can be used for one-time positioning and loading of sustentaculum tail screws,It has higher AOFAS score than conventional surgery.Meanwhile,the guide plate can save the time of C-arm fluoroscopy required for plate model selection and position adjustment,so as to save the surgery time.